the alert for google_product_category was given here:
http://merchant-center-announcements.blogspot.com/2012/02/items-may-soon-fail-to-process-due-to.html

i was able to insert an item using that value.

however, where was that error message seen exactly?
that does not look to be a google-merchant-center error.

if that error is from a third-party implementation
of google's api -- such as magento, xcart, etc.,
then the third-party or third-party forums would
need to be contacted for support.