Okay, I've fixed this by creating an error.php file in the gk_university template package, zipping it up, and then re-installing the template the usual way, from that zip.
I must say, this isn't the type of issue I would expect to have. A missing file in the template package? Looks unprofessional. And your lack of help on this issue has been unfortunate, too, but I'm hoping my post just slipped through the cracks this time.
Thanks, Phil