Thanks for replying back to me, you were offline when I responded previously.
Try creating a new library and see if the problem still occurs.
To create a new library on a Windows PC, hold down the shift key then run iTunes. A dialog will come up and you can create a new library or select an existing one. After making note of where your original library is, create a new one. Bring in some music, then try it again. If it works, you know there is something wrong with your existing library.
Could you try recreating the library on your Mac?
In the Music folder in your home folder, let me know if there is a Library.xml file?
that's alright, you can try it whenever you get a chance, and let me know if it works.