I did some looking around and this appears to be a known bug :
The problem seems related to processes from an old session not terminating correctly, causing Nautilus to be unable to start. None of the suggested solutions/workarounds seem ideal, but they might be worth a try.
1. Kill the bonobo-activation-server as previously described. Check that it has been killed (run the 'ps' command again). Restart Nautilus i.e. log out and back in again or hit CTRL-ALT-BACKSPACE.
2. Remove/rename the following directories ~/.gnome ~/.gnome2 ~/.gconf ~/.gconfd
Restart Nautilus. Be warned that doing this will mean losing any configuration of Gnome you've done yourself and you'll have to do it again.
3. Try using a different Desktop manager e.g. XFCE, KDE
Sorry to not be more help.