Bug#667684: Does "fallen off the bus" continue if you downgrade?

Wed Apr 11 23:27:25 UTC 2012

I've also had fun with a "GPU fell off the bus" message, but it happened 
without any upgrade, and turned out to be caused by a bad video card and 
bad motherboard (yes, both of them were bad, as in moving the card to 
another machine and it'd fail in that machine, and also putting a 
known-working card or brand new card in my machine failed.) Replacing 
both the card and the motherboard fixed it.

That hardware problem came on suddenlyâ€”the machine had been in use for 
over a year before this started happening.

So, I suggest downgrading to 295.20 (e.g., grab it from 
http://snapshot.debian.org, or your /var/cache/apt/archives if you still 
have it there) and making sure it goes away.