How long can an iTunes ringtone be?

I am using iTunes 10.1 (54) and I just created a ringtone that is 28 seconds and it keeps saying that it cannot sync because the duration is too long. I have other ringtones on my phone that are 30 seconds and they don't have any problem. I'm not sure what the problem is. It is the right format (.m4r) so I don't think that is the problem.

Has anyone else had similar issues, and if so, how did you fix it?