I can't think of why you would get those errors on those pages when the hook isn't even being called on those pages in default vbulletin (at least not in 4.0.6). Have you tried turning off ALL other plugins/products except the CMS and your product and seeing if you still get the error?

Have you tried commenting out lines of the code to figure out which one it is having problems with?

Thanks, Lynne. Your comments pointed me in the right direction.

I made some changes in the plug-ins but was still seeing errors. I don't fully understand why but went looking for other products and plugins that might be attaching to postbit hooks. I found an old 3.x add-on (product) that was working fine in the forums but had never been tried in CMS. When I disabled that, the errors disappeared, so obviously there was a conflict at that hook location.

Glad you found it. :)

This was the culprit in my case: https://vborg.vbsupport.ru/showthread.php?t=150761