This is a known bug that hasn't been fixed (I assume that you're using the new version of GForum?)
http://www.gossamer-threads.com/...i?post=260888#260888
Edit: Actually, I've just had a quick look on my site and I think that it appears to be working now. I think the problem may be to do with loading applications in the wrong order in mod_perl. If you are using mod_perl, check the instructions:
http://www.gossamer-threads.com/...i?post=263164#263164
http://www.gossamer-threads.com/...i?post=260888#260888
Edit: Actually, I've just had a quick look on my site and I think that it appears to be working now. I think the problem may be to do with loading applications in the wrong order in mod_perl. If you are using mod_perl, check the instructions:
http://www.gossamer-threads.com/...i?post=263164#263164