Wierd OCI Problem... [Urgent, and please help]

Dear all, My server is running RedHat6.2/Apache 1.3.14/PHP 4.0.4pl1/Oracle 8.0.5. The way I make connection from PHP to Oracle is through php's Oracle 8 extension OCIPLogon. Since the server was made available to the public, *EVERY ONCE A WHILE* I got error messages logged in apache's error log as found in the attachement (sorry the oracle message is in Big5 characters). The error sequence starts with ORA-00022, saying 'invalid session id; access denied', but a connection resource is returned. Then all kinds of ORA-/PLS- errors come after it. The persistent connection affects only the attached apache process, not everyone. That explains when user reload the page, the problem cannot be reproduced everytime. The only way I've found to stop it is by restarting apache. I use quite a lot of Oralce stored procedures and return query results by cursor variables. But I doubt this the reason to it. My guess is that somewhere between apache process and oracle connection is interrupted. I've been working on this issue for a while but got no clue now to move any further. When errors come, the error log got filled up pretty quick. Please help......, and thanks in advance. Chien-pin