Banner manager will not save

I have just taken over a Zen shop. In the banner manager I am able to activate and deactivate existing banners BUT if I either try to create a new banner or edit an existing one it throws me out Admin Home

Just wanted to add to my post as I have still not solved this problem. If I try and save either a new banner or edit an old one it chucks me into admin home. I read a thread:

http://www.zen-cart.com/forum/showthread.php?p=790970

But as I am new to Zen I am a little confused. Does anyone know which files I can try replacing to attempt a fix? Thanks in advance!

Is it just the Banners doing this or does it happen on other things in the Admin?

If it happens to other things in the Admin, then chances are that you recently added the Security Patches:
http://www.zen-cart.com/forum/showthread.php?t=131115

and have mixed up the code, more specifically the files to check:
/includes/functions/html_output.php
/admin/includes/functions/html_output.php

and you need to be sure that you have the right files installed on the server ..