I've been using PS3MS for some years now and has been no trouble apart from being fussy with some .mkv files. My system is all linked by ethernet running through an Apple Time Capsule router. Recently I often get a lost ethernet, cable unplugged warning and usually while watching something. At first I though my trusty old 1st gen TC was packing up but having just bought a new one the problem still happens so it cant be a bad connection. I read that there are issues with the PS3 or even the iMac that's serving to the PS3. Creating a new network location sometimes cures it but as yet not tried that as it happens randomly so will have to watch a run of stuff and see what the debug log says.
So if anyone's had the same issue can you let me know what worked. I'm not sure how to pin it down to one thing?