SERIAL type in PHP

Hi All !

I am get a some problem :

When i write in php
<?php
$dbase=pg_connect("host=somehost.domain.ru user=$login password=$pass
port=5432 dbname=maindb");
$result=pg_Exec($dbase, " CREATE table users (userid serial) ");
?>
my brower ( and log on server ) write to me :

Warning: PostgresSQL query failed: pqReadData() -- backend closed the
channel unexpectedly. This probably means the backend terminated
abnormally before or while processing the request. in
/usr/local/rubin/system/generating.phtml on line 134

I am rewrite:

$dbase=pg_connect("host=somehost.domain.ru user=$login password=$pass
port=5432 dbname=maindb");
$result=pg_Exec($dbase, " CREATE SEQUENCE users_userid_seq ");
$result=pg_Exec($dbase, " CREATE TABLE users ( userid INT4 DEFAULT
nextval('users_userid_seq')) ");
$result=pg_Exec($dbase, " CREATE UNIQUE INDEX users_userid_key on users
(userid) " );

And all work properly. No warnings.

Where is problem ?

Dmitry