Are any of the templates listed here in the style you were using customized:
3.6.10
The error is being caused by not having Security Tokens added inside of your templates. If you manually want to edit these into your templates, read this:
https://vborg.vbsupport.ru/showthread.php?t=177013
You need to find this in all customized vBulletin templates (mainly the ones listed in the above link for 3.6).
Or, you can view updated templates in the ACP and compare and apply changes.