I have recently started getting CTD when I try to load a game while I'm already playing, when Lachance shows up when I'm sleeping to induct me into the guild, and sometimes just at random. Is there some way to tell why this started and to fix it?

Reloading in the middle of the game is a known problem, and the solution is just not to do it. You can exit to main menu and then load a game from there.

As for LaChance, you can look in to the SM-refurbished DLC delayers which change how and when you are inducted into the bad guy guild.

gothemasticator

Actually I got another CTD when I was exiting a castle, so it seems to do it sometimes when the game is loading from a black screen.

Are you sure it's the same CTD, and not a seperate issue?

Hmm I just had a CTD running through a field of grass.

Have you tried http://www.tesnexus.com/downloads/file.php?id=22282? It usually eliminates most CTD's for me. Also usually if it's a specific problem, the CTD has the same crash offset for me, whereas it has another when it's a different problem. So, I'd check that. You can do so by electing to view the report that it wants to send when oblivion crashes.

Yup I use that.

It does sound like you have a couple different kinds of crashes going on:

• repeatable crashes (same circumstances generate a crash fairl reliably), and
  
• random crashes (out in the field, upon loading a new cell)

The repeatable ones you can usually narrow down to the influence of a mod or something like learning not to reload while still in game.

The random ones are the ones we all try to stave off for as long as possible. They can have to do with dirty mods (you can learn about cleaning mods with TES4Edit), running out of memory or graphics memory, overloading the engine by, for instance, running at high speed (or riding a horse) through several cells very quickly, and sometimes even after all we do you just get an occassional crash.

Look for the 50 Steps to a crash free game thread. Also look for a Oblivion and memory usage thread. You can start trying the approaches described there.

gothemasticator

Well before I get into mod cleaning I'll run defragmenter and scan disk and see if that cleans things up.