server process crash

I ocassionally get this error when a large insert is made to a very
large table (Postgres 8.1.9)

Hardware is 8 core Dell 2950 with 6x300G Raid 10 Disk setup.

LOG:  server process (PID 25002) exited with exit code 1
LOG:  terminating any other active server processes
WARNING:  terminating connection because of crash of another server process
DETAIL:  The postmaster has commanded this server process to roll back
the current transaction and exit, because another server process
exited abnormally and possibly corrupted shared memory.

When I vacuum the table and retry the process..it works. The vacuum
output has this warning which indicates that the crash left the table
in an invalid state.

WARNING:  relation "test_dimpart_dimension" page 159809 is
uninitialized --- fixing
WARNING:  relation "test_dimpart_dimension" page 159810 is
uninitialized --- fixing

Why does the crash occur (there were no prior crashes) and can we get
more diagnostics on the actual cause of the error.