I have recently been unable to login to Ubuntu in Unity 3D mode. I can log into Unity 2D mode without problems.

When the problem first started, I checked the log files, and found this in my syslog file around the time I tried to log in:

Code:
Oct 28 17:09:14 beast kernel: [  202.447509] show_signal_msg: 39 callbacks suppressed
Oct 28 17:09:14 beast kernel: [  202.447512] compiz[1939]: segfault at 0 ip           (null) sp 00007fff049bbe88 error 14 in compiz[400000+c000]
Oct 28 17:09:23 beast gnome-session[1873]: WARNING: Application 'compiz.desktop' killed by signal
Oct 28 17:09:23 beast gnome-session[1873]: WARNING: App 'compiz.desktop' respawning too quickly
Oct 28 17:09:23 beast gnome-session[1873]: CRITICAL: We failed, but the fail whale is dead. Sorry....
A little bit of googling suggested I could try fixing the problem by typing

Code:
unity --reset
I tried this, but I still can't log in. However, the error messages about compiz are now gone from my syslog file. In fact I can't find anything in my syslog file that looks like it's reporting an error at the time I try to log in.

Unity 2D still works just fine.

I'm using Ubuntu 12.04 with NVidia proprietary drivers.

Any ideas what to check next?

Thanks
NM