My iTunes shared libraries keep spontaneously disappearing (while I'm listening to them) - sometimes I can listen for 30 or 40 minutes before it happens, other times I can only get a minute or two, but then the shared libraries simply disappear and whatever I'm playing simply stops. The shared libraries tend to reappear after a minute or two, or if I restart iTunes they immediately reappear. This problem happens on multiple shared libraries and persists across restarts and so forth. I'm running 10.5.5 with the latest iTunes. Anyone have any advice?