Long update query ?

Hello,
I have query:
UPDATE userd_session_stat SET status =1 WHERE status=0 AND ((uid <>627 AND
tty <>'ttyA03') OR (uid <> 425 AND tty <> 'ttyA05') OR (uid <> 8011 AND tty
<> 'ttyA09') OR (uid <> 2092 AND tty <> 'ttyA0f') OR (uid <> 249 AND tty <>
'ttyp3') OR (uid <> 249 AND tty <> 'ttyp4') OR (uid <> 249 AND tty <>
'ttyp5') OR (uid <> 249 AND tty <> 'ttyp6'))

But, postgres complains that:
FATAL 1: palloc failure: memory exhausted

I see, the query must be less than 4kB, and this query is less.
Long SELECT queries works fine.
Have any idea? Maybe, I have to change postmaster's settings ? Query
executes from libpg programm.

Thanx,
---------------------------
Sergei Chernev
Internet: ser(at)nsu(dot)ru
Phone: +7-3832-397354