[Koha] Items not checked out report

I've been asked for a list of the top items not checked out from one of my library branches. When I try to run the report, it says NULL instead of giving me the titles although it does say there are items that haven't been checked out. Has anyone else had the same problem and solved it? We're using Koha version 3.06.00.000 on Linux 2.6.31.5-0.1, and I usually use the Google Chrome browser on my Windows computer to access it. Thank you very much! Amber