FROM clause in UPDATE

Hi all,

Could someone tell me why this doesn't work in PostgreSQL 8.1.3 where it
works in v8.0.5 and earlier (i haven't tried versions between these two):

v8.1.3
--------------------------------------------------
-bash-3.00$ psql -c "UPDATE NimrodGridRun
SET status = 'active', control = 'start'
WHERE status not in ('active', 'jsuspend')
AND NimrodGridRun.compute_id = 1
AND NimrodGridRun.agent_id = NimrodAgent.agent_id
AND NimrodAgent.status = 'active'
AND NimrodAgent.tag = '1'"
ERROR: missing FROM-clause entry for table "nimrodagent"
-bash-3.00$

=================================
v8.0.5
----------------------------------------------
[slavisa: talvath - ~ (0)]: psql -c "UPDATE NimrodGridRun
SET status = 'active', control = 'start'
WHERE status not in ('active', 'jsuspend')
AND NimrodGridRun.compute_id = 1
AND NimrodGridRun.agent_id = NimrodAgent.agent_id
AND NimrodAgent.status = 'active'
AND NimrodAgent.tag = '1'"
UPDATE 0

The first query will work if I insert "FROM nimrodagent" just before the
WHERE clause,
Regards,
Slavisa