Sure there is a fix - make sure you completely uninstall any mods you are no longer using or that you completely install any mods that you have. It looks like it is related to the thankyou mod since it calls for the function set_thankscache which is not a vbulletin function.
If you continue to have problems with it, you need to ask for help in the modification thread since that is where support for modifications is given.
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