Squeezecenter does not support UPnP prototocal.  On v. 6.54 it worked just fine.  Please see the description of the problem below:

The current and previous version of SlimServer has a configuration
(somewhere under the "Network" settings) named something like "Should
SlimServer look for other UPnP media servers on your network?".

In the old version (6.54) this option works; in the new version it does
not work. Meaning the old version will connect to Rhapsody via UPnP and play songs imported into Rhapsody from the hard drive, the new version on the other hand, even with this option enabled, does not access anything from the harddrive thru Rhapsody.

All of the files that come directly from the Rhapsody server are OK and play
fine, but thinking of my computer as as the server for the files on my
harddrive that I have imported into Rhapsody, these do not play through
squeezebox. The reason I want this function back is to make a playlist with
music that I get from the Rhapsody server and music that I get from my hard
drive that is not available thru Rhapsody. For instance, Rhapsody has a
great collection of music, but no Beatles. To get those on a combined
playlist, I buy the CD rip it to my hard drive in MP3 format and then import
those into Rhapsody. I don't think the MP3 files are copied into Rhapsody,
but that Rhapsody creates a link or pointer to the files so that they can be
played through their player and included in a playlist with Rhapsody music
as well.