Do you have the iTunes Music folder added to the Sharing system preferences? Make sure File Sharing is checked and add the folder to the list of Shared Folders on the right. Also check the Users listed for that folder and make certain Everyone has at least Read Only access.
I just tried this on my network and I have the same problem. 😕 With some searching it seems maybe the only solution is to move the iTunes Music folder into the Public, or Shared folders.