Nicole,
Not being able to move courses to different categories seems to be a general problem. It was reported again here:
http://moodle.org/mod/forum/discuss.php?d=16452#78392
I don't have a solution, but thought you would like to know it's probably not related to your changes to the code.
Sylvia
Testing and QA
Hacking Moodle Course Display
Dyskusyjŏ ôstała zaszperowanŏ, tōż niy możesz już ôdpedzieć.