Hi!
When I try to open the music library in WMC I get the message: "A necessary component of Windows Media Center is currently not available. Please restart Windows Media Center". Uninstalling MCC_MC_ADDIN and rebooting fixed the problem. I re-installed the component, rebooted, and the problem was there again.
I can't remember having seen this message before v156. This doesn't mean it wasn't there, though.
ccristal