Stability problems

Hi,
I have strange stability problems.
I can't access a table (the table is different each time I get the
problem, it could be a system table (pg_am), or a user defined one):
Can't "select *" the whole table but can "select * limit x offset y", so
it appears that only a tuple is in bad status. I can't vacuum or pg_dump
this table too.
The error disappears after waiting some time.

I get the following error in log when select the 'bad' line:
------------------------------------------------------------------------
----
2002-11-05 11:26:42 [3062] DEBUG: server process (pid 4551) was
terminated by signal 11
2002-11-05 11:26:42 [3062] DEBUG: terminating any other active server
processes
2002-11-05 11:26:42 [4555] FATAL 1: The database system is in
recovery mode
2002-11-05 11:26:42 [3062] DEBUG: all server processes terminated;
reinitializing shared memory and semaphores
2002-11-05 11:26:42 [4557] DEBUG: database system was interrupted at
2002-11-05 11:23:00 CET
------------------------------------------------------------------------
----

I get the following error in log when vacuuming the 'bad' table:
------------------------------------------------------------------------
----
2002-11-05 14:46:44 [5768] FATAL 2: failed to add item with len = 191
to page 150 (free space 4294967096, nusd 0, noff 0)
2002-11-05 14:46:44 [5569] DEBUG: server process (pid 5768) exited
with exit code 2
2002-11-05 14:46:44 [5569] DEBUG: terminating any other active server
processes
2002-11-05 14:46:44 [5771] NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend
died abnormally and possibly corrupted shared memory.
I have rolled back the current transaction and am
going to terminate your database system connection and exit.
Please reconnect to the database system and repeat your query.
2002-11-05 14:46:44 [5772] NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend
died abnormally and possibly corrupted shared memory.
I have rolled back the current transaction and am
going to terminate your database system connection and exit.
Please reconnect to the database system and repeat your query.
2002-11-05 14:46:44 [5569] DEBUG: all server processes terminated;
reinitializing shared memory and semaphores
2002-11-05 14:46:44 [5774] DEBUG: database system was interrupted at
2002-11-05 14:46:40 CET
------------------------------------------------------------------------
----

template1=# select version();
PostgreSQL 7.2.1 on i686-pc-linux-gnu, compiled by GCC 2.96

Is it a lock problem? Is there a way to log it?

Thanks for all making such a good job.

Nicolas VERGER