First of all; you don't get these errors when browsing the site yourself?
Assuming "no"; Although I have not been able to reproduce the error and it does not seem to be a general one (as with a lot of issues this is specific to the javascript/ CSS that themes & plugins insert), I've seen one other user with a similar problem with errors thrown when GoogleBot visited his site.
The solution in that thread would be applicable to your problem as well (except you might have to change the useragent name to the one used by Google Pagespeed Insights).
Hope this helps,
frank