[Koha] Problem checking out to some patrons

Here's an odd issue. We are running 3.0.05 (Zebra), and everything is going pretty smoothly. A new problem has come up, though, that Koha won't let us check out to some patrons. When we scan or type in a barcode, a thin yellow box--the kind that usually contain message dialoges--appears with no information. It doesn't matter what items we scan, it always returns to the same screen without checking the item out. Here is a link to screenshot so you can see exactly what we are talking about: http://www.lru.edu//UserFiles/Documents/Library/kohascreenshot.jpg There are no error messages in any of the logs in /var/log/koha. The only way we have been able to resolve the issue is to delete the account and recreate it. Thoughts?