Well as of the new vb4 template version you broke the search system. If you use quick search or try to search without explicitly applying filters you wont get a result because the search term itself gets lost.
After reviewing the code for some reason you updated a few of the search term related fields to GPC query instead of text.
With these changes you are now able to search for items correctly. We am really not sure why this was changed between 2.1.0a1 and 2.1.0 as if you check the 2.1.0a1 files things are validated using the correct name and we were unable to locate any other search related changes for the field name to point to it was an intended change.
Disregard as I noticed it was reported in the bug tracker on vbulletin.com