Problem with domino server on scheduling agent

Recently after upgrading our Domino server to version 6.5.1, I have run into some errors. During installation I enabled the scheduling agent and had the admin as the signer of the code.
The problem is that the weekly scheduled agent is not functioning in accordance with the timing. When you configure it to run once a week it fails to do so yet when you configure it to run after a few hours let’s say two hours from that instant it will run. I would be glad to receive some help.
