You're using Vista or Windows7 right?
Installing the game in Program Files causes all sorts of problems. The easiest/fastest method of correction is to just http://www.gamesas.com/index.php?/topic/781497-vistawindows-7-problems/page__p__11352753entry11352753
I'm using Win7. My question is, what if that doesn't fix the issue? For instance, I use the mod "World of Faces" by GhanBuriGhan, I use the .esm version (if you have any idea what I'm talking about). I've reinstalled it and MW, and the thing still has mesh and texture error messages... and it seems to me they are becoming worse! I walked into Balmora Mages Guild, and Ranis Athrys' head was gone - it was there yesterday! My WinXP laptop had no such problems, and I originally took the zipped archive from it's Downloads folder, and installed it on the Win7 desktop to a non-Prog Files location. Thinking maybe the 7zip was corrupted, I re-DL'd, but the problem persists.
I don't know if this should be it's own topic, it matches the title, so far as I can see.