5.1 RELEASE - Panic

[freebsd at sentinelchicken.net]

I am currently running 5.1 RELEASE, as system I recently 'downgraded' from CURRENT.  Since I moved back to RELEASE, the system has been giving me file 
system errors from time to time.  I've run fsck - though I know very little of what I'm going with this utility.  And now, I'm getting a PANIC, with 
the following error:

mode = 041777, inum = 3, fs = /usr
panic: ffs_valloc: dup alloc
Debugger("panic")
Stoped at    Debugger+0x4d:  xchgl  %ebx,in_Debugger.0

I ran CURRENT on this system for 6-8 months and never got a panic - the system is not used all that often.

Anyone have any suggestions as to what I can do?


Thanks,
Jason