Changes to Admin Configuration menu is not working

Hello,
I'm using ZC 1.3.8a Patch: 1:: Database Patch Level: 1.3.8

I've been trying to modify a setting under Admin/Modules/Payment for the Paypal IPN Websites Payment Standard feature. Specifically I've been trying to add the PDT Token information. When I paste the token in from my Paypal account, and then hit "Update", the screen immediately goes back to the Admin Panel "home page". The additions/changes are not showing, only what was originally there.

This is also the same for any feature of this kind where changes are being made (ie, trying to enable the "Send Low Stock Emails" from 0 to 1 does not take).

I've never encountered this before in this store or my other store, and am at total loss as how to fix it or even where to look. :unsure: Please help if you can! Many thanks!

Review the similar threads below
What I have seen is that you have not applied the patch completely or correctly

Thanks Kobra. I went back and checked the html_output.php file that was changed manually with the security patch. The only difference I could see was in the line that needed to be added, I have "$_session['securityToken']. I changed the "session" to upper case and added a line space after it and everything worked fine. I didn't realize it was case sensitive...

Thanks much as always for your help!!