Some further things to check:

Does venus still function - can you 'cd /coda && ls' ?

Does venus still communicate with the servers in an unauthenticated
mode?  Can you 'cfs cs'?

What does 'codacon?' say?

What does 'cfs lv' say?  Are you disconnected?

When one client fails, are the others still connected?

Can you fetch new files (make some with System:AnyUser rl permissions)?

If you have built from source, gdb the venus binary and attach to the
process, and look at the backtrace?

shutdown venus (vutil shutdown) and restart it.  Does this help?

Are auth2 and codasrv running on the server?  Are they ok?  Does
restarting them help?

What operating system?  What version?  What venus version?

        Greg Troxel <gdt_at_ir.bbn.com>