– Conflict between mods
Solution: Disable mods one at a time until your game doesn’t crash anymore (or crashes less). Do not save over your current game while testing – create new test saves.
– Bad load order between mods
Solution: Study Readme files for your mods and use Oblivion Mod Manager (OBMM) to move mods around. There are a few pages of hints about how to find a good load order (look at the Forum FAQ).
– Mod Incompletely Installed
Solution: Try to identify if something is causing crashes in particular (entering a house, talking to an NPC in particular, etc…) to identify which mod is causing this and reinstall the mod in question.
– Bug in a Mod
Solution: Check out the comments section of the downloaded mod (most places like TES Source, Elric, etc… have comments sections for each mod) or look for mod threads in the official forum. If you can’t find anything, ask in the forum if this is a known bug. Have your list of installed mods ready when you ask.
– Fragmented Hard Drive
Solution: Keep extra room available on your system and your Oblivion drives (if they are separate). Keep both drives frequently defragmented (once a week). Some software such as Diskeeper have options to keep drives automatically defragmented based on usage.
– Slow Hard Drive
Solution: Use utilities such as HD Tack to find which one of your drive is the fastest. Install Oblivion on that drive or buy a new drive if you don’t have anything fast enough.
– Insufficient Memory
Solution: If you are going to use a lot of mods, in particular graphic / textures enhancers, make sure your video card has at least 512M of RAM and your machine at least 1 Gb (2 Gb is better).
– Tasks running in background while Oblivion is playing (email, spyware scans, antivirus scan)
Solution: Disable anything you can find that is not necessary to your system while you are playing. Oblivion doesn’t like to be distracted by something else on your computer, especially if other tasks compete for drive access with it.
– Video Drivers or other known issue with the base game
Solution: Stay up to date on your video drivers. Check out the official forums to find out if there are known issues between Oblivion and your video card.
– Bad Archive Invalidation for meshes or textures
Solution: Make sure new meshes and textures introduced by mods are correctly registered with the game. Use either the ‘OBMM BSA updater’ or the ‘Archive Invalidation Invalidated!’ method to keep your game up to date.
– Corrupted Saved Game
Solution: Avoid using Quick Save or saves during combat. Use plain saves, if possible one per playing session. Create a new save when you start playing and overwrite it from time to time until you are done. Then create a new save just before quitting the game.