I had similar issues with the Samsung BD-C6500 blu ray player. PC Share manager would work fine from my old XP laptop but as soon as I tried to stream from my new Vista Ultimate 64 bit desktop, I couldn't get 2 minutes into the movie before a message popped up that PC Share Manager Disconnected. I was pulling my hair out. I think I may have solved the problem. So far so good. I'm about 20 minutes into a movie and no problem.
Scenario: My Vista desktop had 2 NIC's. 1 a realtek onboard which I had disabled because I had been using a Killer NIC for quite some time for gaming. I just re-enabled my Realtek onboard and disconnected my Killer NIC and all seems fine now. The Killer NIC has it's own brain and firewall and stuff, so I'm pretty sure that was the problem.
Movie is still going.
If anyone has a Killer NIC or similar card, I would try changing to something barebone or play around with the software for the NIC card. I was thinking it was the BLU RAY player or something to do with Vista, since it worked good on my XP laptop. But, that doesn't seem to be the case. Damn Killer NIC.
Movie still going. 30 minutes in now.
Like I said, I couldn't get 2 minutes in before disconnect so I am fairly confident that this will be my fix and hopefully it helps others too.
Good luck all!