ORA-01801

My application is running 24 hours a day on HP-UNIX machine.
Every week i receive the error ORA - 01801 and after shutdown the database and reboot the server, the problem disappear. The oracle documentation about it does not help a lot.
What can i do to solve this problem forever?


Thanks
Alexandre

What version of Oracle are you using? What is being done when you receive this error? I found quite a bit about this on Metalink.