pqReadData() -- backend closed the channel unexpectedly (huh?)

Hello all:

I have a simple database which is now exhibiting some strange symptoms.
The most obviously sick is where I try to delete a record in a table, and
get the response:

pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.

I dropped the database, and restored it from a backup. Same results.
Vacuum analyze doesn't complain. I turned on debug messages from the
postmaster, but didn't see anything that pointed to the problem. For the
record, the log shows:

StartTransactionCommand
query: SELECT usesuper FROM pg_user WHERE usename = 'fpm'
ProcessQuery
CommitTransactionCommand
StartTransactionCommand
query: select * from units ;
ProcessQuery
CommitTransactionCommand
StartTransactionCommand
query: delete from units where unit_id = 5;
ProcessQuery
/opt/pgsql/bin/postmaster: reaping dead processes...
/opt/pgsql/bin/postmaster: CleanupProc: pid 21004 exited with status 139
Server process (pid 21004) exited with status 139 at Tue Nov 7 11:04:56 2000
Terminating any active server processes...
Server processes were terminated at Tue Nov 7 11:04:56 2000
Reinitializing shared memory and semaphores
shmem_exit(0)
binding ShmemCreate(key=52e325, size=1104896)
/opt/pgsql/bin/postmaster: ServerLoop: handling reading 5
/opt/pgsql/bin/postmaster: ServerLoop: handling reading 5
DEBUG: Data Base System is starting up at Tue Nov 7 11:04:56 2000
DEBUG: Data Base System was interrupted being in production at Tue Nov 7 11:04:40 2000
/opt/pgsql/bin/postmaster: ServerLoop: handling writing 5
The Data Base System is starting up
/opt/pgsql/bin/postmaster: ServerLoop: handling writing 5
DEBUG: Data Base System is in production state at Tue Nov 7 11:04:56 2000
proc_exit(0)
shmem_exit(0)
exit(0)
/opt/pgsql/bin/postmaster: reaping dead processes...

Version: 7.0.2.

Any suggestions on how/where to look for the source of the problem?

Thanks....

-frank