I installed a second copy of Oblivion to another location, but it overwrote the registry files for the old one... and now, everything is pretty much... broken.
http://www.google.com/search?btnG=1&q=wat+do

To elaborate more... The error was originally "unable to find masterfile oblivion.esm", so I replaced it with the one from my original installation. Now when I load a save... the whole thing loads, then, instant CTD.

several options :

1. move the old files to the new location -- by doing this the old files will overwrite the new ones but will be in the location that the registry points to !

2. edit the registry using regedit and change the install location back to the old location - this will have the registry be able to find the old install

3. uninstall the new files using the uninstaller and then rename the old folder - install again to the old folder name - delete the new install and rename your old install (this updates the registry info and gets you back to the old install

etc.

Regedit... Why didn't I think of that...? Corruption madness I suppose.

Ok none of those worked. I believe I may be completely screwed.

I've tried everything. Uninstalling, reinstalling... multiple times, cleaning the registry... all that crap, but I still have a problem. As mentioned in an earlier post, once a save fully loads, CTD. I'm at a loss here.

Missing master? When you uninstalled, did you delete the oblivion folders? (both install folders, and the one in My Games?)

Only the one in Program Files.

If you installed it back into the directory you did NOT delete..... the uninstaller won't remove files that weren't there with the stock game. So, any mods etc, that you installed will still be there. Tends to confuse the game.

I installed it to a new directory as well, but that one gives me an instant CTD on startup.

I got it working. It was, to my knowledge, some kind of mix-up in the my games/oblivion directory. I moved all of the files in there to another location, and had the game regenerate them, and everything was fine. I'm not so sure it was an oblivion.ini error though, as I looked through there multiple times and didn't spot anything suspicious.