The following will help you fix things in case your Manifest.ini file gets corrupted. This can happen by badly written/installed Umod files.
Make sure that the following lines and sections exist in your Manifest.ini. This assumes you have patched your UT to version 405B.
The Manifest.ini
[Setup] MasterProduct=UnrealTournament Group=UnrealTournament Group=Unreal Tournament [UnrealTournament] File=System\Core.u File=System\Core.dll File=System\Core.int File=System\D3DDrv.dll File=System\D3DDrv.int File=System\Engine.dll File=System\Engine.int File=System\Engine.u File=System\Fire.dll File=System\Fire.u File=System\Galaxy.dll File=System\Galaxy.int File=System\GlideDrv.dll File=System\GlideDrv.int File=System\IpDrv.dll File=System\IpDrv.int File=System\IpDrv.u File=System\IpServer.u File=System\IpServer.int File=System\MeTaLDrv.dll File=System\MeTaLDrv.int File=System\MSVCRT.dll File=System\OpenGlDrv.dll File=System\OpenGlDrv.ini File=System\OpenGlDrv.int File=System\Render.dll File=System\RunServer.bat File=System\Setup.exe File=System\Setup.int File=System\SGLDrv.dll File=System\SGLDrv.int File=System\SoftDrv.dll File=System\SoftDrv.int File=System\Startup.int File=System\UCC.exe File=System\Window.dll File=System\Window.int File=System\WinDrv.dll File=System\WinDrv.int File=System\Botpack.int File=System\CommandoSkins.int File=System\FCommandoSkins.int File=System\SGirlSkins.int File=System\SoldierSkins.int File=System\UnrealTournament.exe File=System\UnrealTournament.icd File=System\UnrealTournament.int File=System\UnrealI.int File=System\UnrealI.u File=System\UnrealShare.int File=System\UnrealShare.u File=System\BotPack.u File=System\UBrowser.u File=System\UBrowser.int File=System\UTBrowser.u File=System\UWindow.u File=System\UMenu.u File=System\UMenu.int File=System\UTMenu.u File=System\UTMenu.int File=System\UTServerAdmin.int File=System\UTServerAdmin.u File=System\UWeb.int File=System\UWeb.u File=System\UWeb.dll File=System\DefUser.ini File=System\User.ini File=System\Default.ini File=System\UnrealTournament.ini File=System\UnrealTournamentWeb.url File=System\NetGamesUsaWeb.url File=System\GlobalStatsWeb.url File=Textures\Belt_fx.utx File=Textures\LadderFonts.utx File=Textures\UWindowFonts.utx File=Textures\LadrArrow.utx File=Textures\LadrStatic.utx File=Web\current.uhtm File=Web\current_console.uhtm File=Web\current_console_log.uhtm File=Web\current_console_send.uhtm File=Web\current_game.uhtm File=Web\current_menu.uhtm File=Web\current_mutators.uhtm File=Web\current_players.uhtm File=Web\defaults.uhtm File=Web\defaults_bots.uhtm File=Web\defaults_ippolicy-d.uhtm File=Web\defaults_ippolicy-f.uhtm File=Web\defaults_ippolicy-h.uhtm File=Web\defaults_maps.uhtm File=Web\defaults_menu.uhtm File=Web\defaults_rules.uhtm File=Web\defaults_server.uhtm File=Web\defaults_settings.uhtm File=Web\menu.uhtm File=Web\message.uhtm File=Web\root.uhtm File=Web\plaintext\current.uhtm File=Web\plaintext\current_console.uhtm File=Web\plaintext\current_console_log.uhtm File=Web\plaintext\current_console_send.uhtm File=Web\plaintext\current_game.uhtm File=Web\plaintext\current_menu.uhtm File=Web\plaintext\current_mutators.uhtm File=Web\plaintext\current_players.uhtm File=Web\plaintext\defaults.uhtm File=Web\plaintext\defaults_bots.uhtm File=Web\plaintext\defaults_ippolicy-d.uhtm File=Web\plaintext\defaults_ippolicy-f.uhtm File=Web\plaintext\defaults_ippolicy-h.uhtm File=Web\plaintext\defaults_maps.uhtm File=Web\plaintext\defaults_menu.uhtm File=Web\plaintext\defaults_rules.uhtm File=Web\plaintext\defaults_server.uhtm File=Web\plaintext\defaults_settings.uhtm File=Web\plaintext\menu.uhtm File=Web\plaintext\message.uhtm File=Web\plaintext\root.uhtm File=Web\images\1-1.gif File=Web\images\1-2.gif File=Web\images\1.gif File=Web\images\2-1.gif File=Web\images\2-2.gif File=Web\images\3-1.gif File=Web\images\3-2.gif File=Web\images\4-1.gif File=Web\images\4-2.gif File=Web\images\5-1.gif File=Web\images\5-2.gif File=Web\images\6-1.gif File=Web\images\6-2.gif File=Web\images\7-1.gif File=Web\images\7-2.gif File=Web\images\7-3.gif File=Web\images\image.gif File=Web\images\logo.gif File=Web\images\m1-1.gif File=Web\images\m1-2.gif File=Web\images\m3-1.gif File=Web\images\m3-2.gif File=Web\images\right.gif File=Help\Logo.bmp File=Help\Unreal.ico File=Help\UnrealEd.ico File=Help\UnrealTournamentSetupLogo.bmp File=Help\UnrealTournamentLogo.bmp File=Help\ReadMe.htm File=Help\Heat.ico File=Help\MPlayer.ico File=Maps\AS-Frigate.unr File=Maps\AS-Guardia.unr File=Maps\AS-HiSpeed.unr File=Maps\AS-Mazon.unr File=Maps\AS-OceanFloor.unr File=Maps\AS-Overlord.unr File=Maps\AS-Rook.unr File=Maps\AS-Tutorial.unr File=Maps\CityIntro.unr File=Maps\CTF-Command.unr File=Maps\CTF-Coret.unr File=Maps\CTF-Dreary.unr File=Maps\CTF-EternalCave.unr File=Maps\CTF-Face.unr File=Maps\CTF-Gauntlet.unr File=Maps\CTF-LavaGiant.unr File=Maps\CTF-Niven.unr File=Maps\CTF-November.unr File=Maps\CTF-Tutorial.unr File=Maps\DM-Barricade.unr File=Maps\DM-Codex.unr File=Maps\DM-Conveyor.unr File=Maps\DM-Curse][.unr File=Maps\DM-Deck16][.unr File=Maps\DM-Fetid.unr File=Maps\DM-Fractal.unr File=Maps\DM-Gothic.unr File=Maps\DM-Grinder.unr File=Maps\DM-HyperBlast.unr File=Maps\DM-KGalleon.unr File=Maps\DM-Liandri.unr File=Maps\DM-Morbias][.unr File=Maps\DM-Morpheus.unr File=Maps\DM-Oblivion.unr File=Maps\DM-Peak.unr File=Maps\DM-Phobos.unr File=Maps\DM-Pressure.unr File=Maps\DM-Pyramid.unr File=Maps\DM-Stalwart.unr File=Maps\DM-StalwartXL.unr File=Maps\DM-Tempest.unr File=Maps\DM-Turbine.unr File=Maps\DM-Tutorial.unr File=Maps\DM-Zeto.unr File=Maps\DOM-Cinder.unr File=Maps\DOM-Condemned.unr File=Maps\DOM-Cryptic.unr File=Maps\DOM-Gearbolt.unr File=Maps\DOM-Ghardhen.unr File=Maps\DOM-Lament.unr File=Maps\DOM-Leadworks.unr File=Maps\DOM-MetalDream.unr File=Maps\DOM-Olden.unr File=Maps\DOM-Sesmar.unr File=Maps\DOM-Tutorial.unr File=Maps\Entry.unr File=Maps\EOL_Assault.unr File=Maps\EOL_Challenge.unr File=Maps\EOL_CTF.unr File=Maps\EOL_Deathmatch.unr File=Maps\EOL_Domination.unr File=Maps\EOL_Statues.unr File=Maps\UT-Logo-Map.unr File=Maps\UTCredits.unr File=Music\Botmca9.umx File=Music\Botpck10.umx File=Music\Cannon.umx File=Music\Colossus.umx File=Music\Course.umx File=Music\Credits.umx File=Music\Ending.umx File=Music\Enigma.umx File=Music\firebr.umx File=Music\Foregone.umx File=Music\Godown.umx File=Music\Lock.umx File=Music\Mech8.umx File=Music\Mission.umx File=Music\Nether.umx File=Music\Organic.umx File=Music\Phantom.umx File=Music\Razor-ub.umx File=Music\Run.umx File=Music\SaveMe.umx File=Music\Savemeg.umx File=Music\Seeker.umx File=Music\Seeker2.umx File=Music\Skyward.umx File=Music\Strider.umx File=Music\Suprfist.umx File=Music\UnWorld2.umx File=Music\utmenu23.umx File=Music\Uttitle.umx File=Music\Wheels.umx File=Sounds\Activates.uax File=Sounds\Addon1.uax File=Sounds\AmbAncient.uax File=Sounds\AmbCity.uax File=Sounds\AmbModern.uax File=Sounds\AmbOutside.uax File=Sounds\Announcer.uax File=Sounds\BossVoice.uax File=Sounds\DDay.uax File=Sounds\DMatch.uax File=Sounds\DoorsAnc.uax File=Sounds\DoorsMod.uax File=Sounds\Extro.uax File=Sounds\Female1Voice.uax File=Sounds\Female2Voice.uax File=Sounds\FemaleSounds.uax File=Sounds\LadderSounds.uax File=Sounds\Male1Voice.uax File=Sounds\Male2Voice.uax File=Sounds\MaleSounds.uax File=Sounds\noxxsnd.uax File=Sounds\openingwave.uax File=Sounds\Pan1.uax File=Sounds\rain.uax File=Sounds\TutVoiceAS.uax File=Sounds\TutVoiceCTF.uax File=Sounds\TutVoiceDM.uax File=Sounds\TutVoiceDOM.uax File=Sounds\VRikers.uax File=Textures\ArenaTex.utx File=Textures\BossSkins.utx File=Textures\castle1.utx File=Textures\city.utx File=Textures\commandoskins.utx File=Textures\Coret_FX.utx File=Textures\Creative.utx File=Textures\credits.utx File=Textures\Crypt2.utx File=Textures\Crypt_FX.utx File=Textures\CTF.utx File=Textures\DacomaFem.utx File=Textures\DacomaSkins.utx File=Textures\DDayFX.utx File=Textures\DecayedS.utx File=Textures\DMeffects.utx File=Textures\Egypt.utx File=Textures\EgyptPan.utx File=Textures\eol.utx File=Textures\Faces.utx File=Textures\FCommandoSkins.utx File=Textures\Female1Skins.utx File=Textures\Female2Skins.utx File=Textures\FlareFX.utx File=Textures\FractalFX.utx File=Textures\GothFem.utx File=Textures\GothSkins.utx File=Textures\Indus1.utx File=Textures\Indus2.utx File=Textures\Indus3.utx File=Textures\Indus4.utx File=Textures\Indus5.utx File=Textures\Indus6.utx File=Textures\Indus7.utx File=Textures\Lian-X.utx File=Textures\Logo.utx File=Textures\Male1Skins.utx File=Textures\Male2Skins.utx File=Textures\Male3Skins.utx File=Textures\Metalmys.utx File=Textures\Mine.utx File=Textures\NivenFX.utx File=Textures\of1.utx File=Textures\Old_FX.utx File=Textures\Palettes.utx File=Textures\PhraelFx.utx File=Textures\RainFX.utx File=Textures\RotatingU.utx File=Textures\Scripted.utx File=Textures\SGirlSkins.utx File=Textures\ShaneChurch.utx File=Textures\SkTrooperSkins.utx File=Textures\SkyBox.utx File=Textures\Slums.utx File=Textures\Soldierskins.utx File=Textures\TrenchesFX.utx File=Textures\UT.utx File=Textures\UTbase1.utx File=Textures\UTcrypt.utx File=Textures\UTtech1.utx File=Textures\UTtech2.utx File=Textures\UTtech3.utx File=Textures\UT_ArtFX.utx File=Textures\XbpFX.utx File=Textures\Xtortion.utx File=Textures\AlfaFX.utx File=Textures\Ancient.utx File=Textures\BluffFX.utx File=Textures\ChizraEFX.utx File=Textures\Crypt.utx File=Textures\Detail.utx File=Textures\FireEng.utx File=Textures\GenEarth.utx File=Textures\GenFluid.utx File=Textures\GenFX.utx File=Textures\GenIn.utx File=Textures\GenTerra.utx File=Textures\GenWarp.utx File=Textures\GreatFire.utx File=Textures\GreatFire2.utx File=Textures\HubEffects.utx File=Textures\ISVFX.utx File=Textures\JWSky.utx File=Textures\LavaFX.utx File=Textures\Liquids.utx File=Textures\MenuGr.utx File=Textures\NaliCast.utx File=Textures\NaliFX.utx File=Textures\PlayrShp.utx File=Textures\Queen.utx File=Textures\Render.utx File=Textures\ShaneDay.utx File=Textures\ShaneSky.utx File=Textures\Skaarj.utx File=Textures\SkyCity.utx File=Textures\SpaceFX.utx File=Textures\Starship.utx File=Textures\TCrystal.utx File=Textures\Terranius.utx File=Textures\XFX.utx File=System\UnrealEd.exe File=System\Editor.dll File=System\Editor.int File=System\Editor.u File=System\mplaynow.exe File=System\mplaynow.ini File=System\mput.mpi File=System\GotoHeat.exe Backup=System\Core.dll Backup=System\Core.int Backup=System\Window.dll Backup=System\Window.int Backup=System\Setup.exe Backup=System\Setup.int Backup=System\Manifest.ini Backup=Help\Logo.bmp Delete=System\Detected.log Delete=System\Detected.ini Delete=System\UnrealTournament.log Delete=System\Unreal.log Delete=System\Editor.log WinRegistry=HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall\UnrealTournament\DisplayName WinRegistry=HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall\UnrealTournament\UninstallString Folder=Maps Folder=Textures Folder=Sounds Folder=Music Shortcut=C:\WINDOWS\Start Menu\Programs\Unreal Tournament\Play Unreal Tournament.lnk Shortcut=C:\WINDOWS\Start Menu\Programs\Unreal Tournament\Unreal Tournament Safe Mode.lnk Shortcut=C:\WINDOWS\Start Menu\Programs\Unreal Tournament\Documentation.lnk Shortcut=C:\WINDOWS\Start Menu\Programs\Unreal Tournament\Unreal Tournament Web Page.lnk WinRegistry=HKEY_CLASSES_ROOT\.unr\ WinRegistry=HKEY_CLASSES_ROOT\.unreal\ WinRegistry=HKEY_CLASSES_ROOT\.umod\ WinRegistry=HKEY_CLASSES_ROOT\unreal\ WinRegistry=HKEY_CLASSES_ROOT\unreal\URL Protocol WinRegistry=HKEY_CLASSES_ROOT\unreal\DefaultIcon\ WinRegistry=HKEY_CLASSES_ROOT\unreal\Shell\ WinRegistry=HKEY_CLASSES_ROOT\unreal\Shell\open\ WinRegistry=HKEY_CLASSES_ROOT\unreal\Shell\open\command\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Link\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Link\DefaultIcon\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Link\Shell\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Link\Shell\open\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Link\Shell\open\command\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Map\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Map\DefaultIcon\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Map\Shell\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Map\Shell\open\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Map\Shell\open\command\ WinRegistry=HKEY_LOCAL_MACHINE\Software\Unreal Technology\Installed Apps\UnrealTournament\Folder WinRegistry=HKEY_LOCAL_MACHINE\Software\Unreal Technology\Installed Apps\UnrealTournament\Version WinRegistry=HKEY_CLASSES_ROOT\Unreal.Module\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Module\DefaultIcon\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Module\Shell\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Module\Shell\open\ WinRegistry=HKEY_CLASSES_ROOT\Unreal.Module\Shell\open\command\ Shortcut=C:\WINDOWS\Start Menu\Programs\Unreal Tournament\Play Unreal Tournament on mplayer.com.lnk Shortcut=C:\WINDOWS\Start Menu\Programs\Unreal Tournament\Play Unreal Tournament on HEAT.lnk Caption=Unreal Tournament Version=400 [Unreal Tournament] File=system\window.dll File=system\core.dll File=system\setup.exe File=Help\ReleaseNotes.htm File=System\BossSkins.int File=system\botpack.u File=system\core.u File=system\d3ddrv.dll File=system\d3ddrv.int File=system\default.ini File=system\defuser.ini File=system\editor.dll File=system\editor.u File=system\engine.dll File=system\engine.u File=system\fire.dll File=system\fire.u File=system\galaxy.dll File=system\glidedrv.dll File=system\ipdrv.dll File=system\ipdrv.u File=system\ipserver.u File=system\render.dll File=system\softdrv.dll File=system\ubrowser.u File=system\ucc.exe File=system\umenu.u File=system\utbrowser.u File=system\utmenu.u File=system\utserveradmin.u File=system\uweb.dll File=system\uweb.u File=system\uwindow.u File=system\windrv.dll File=System\Engine.int File=System\MeTaLDrv.dll File=System\MeTaLDrv.int File=system\opengldrv.dll File=System\SGLDrv.dll File=System\00000409.016 File=System\00000409.256 File=System\clcd16.dll File=System\clcd32.dll File=System\clokspl.exe File=System\dplayerx.dll File=System\drvmgt.dll File=System\secdrv.sys File=System\unrealtournament.exe File=System\unrealtournament.icd Backup=System\Core.dll Backup=System\Core.int Backup=System\Window.dll Backup=System\Window.int Backup=System\Setup.exe Backup=System\Setup.int Backup=System\Manifest.ini Backup=Help\UnrealTournamentSetupLogo.bmp Caption=Unreal Tournament Version=405B Requires=UnrealTournament