panic (cpu 0): kernel memory fault

I just noticed that one of our Tru64 systems had rebooted itself a couple
of days ago.  I found the following the /var/adm/messages :


Apr 21 21:12:20 cams1 vmunix:
Apr 21 21:12:20 cams1 vmunix: trap: invalid memory read access from kernel
mode
Apr 21 21:12:20 cams1 vmunix:
Apr 21 21:12:20 cams1 vmunix:     faulting virtual address:
0x0000000000000000
Apr 21 21:12:20 cams1 vmunix:     pc of faulting instruction:
0xfffffc0000645ad4
Apr 21 21:12:20 cams1 vmunix:     ra contents at time of fault:
0xfffffc00005c2f14
Apr 21 21:12:20 cams1 vmunix:     sp contents at time of fault:
0xfffffe0544e575f0
Apr 21 21:12:20 cams1 vmunix:
Apr 21 21:12:20 cams1 vmunix: panic (cpu 0): kernel memory fault
Apr 21 21:12:20 cams1 vmunix: syncing disks... done


Does anyone know what the cause of the above is?  This system has been
running fine for years without problems.  Does this indicate a hardware
problem, such as with the system's memory or CPU ?


Thanks,


        ---Andy