System V is Crashing

[mlip at nadc.ARPA]

A colleague of mine is trying to bring up AT&T's UNIX System V on a VAX
11/780.  Periodically, the system will crash and halt the CPU with the
following message:

Machine software error: Protection violation on interrupt stack.

AT&T insists that the crash is due to a hardware error.  However, this
same VAX can run UNIX 4.1BSD and VMS with no problems.  Any clues to the
cause of this problem would be immensely appreciated.

Thank You,
mlip at nadc (Michael Lipczynski)