I've done a bit of research on this issue between members of my clan and public players playing on our servers.
It comes down to this:
If you are running Vista 64bit with a Geforce card, you will always return black SS. Any other type of operating system with updated vcard drivers, Direct X updates will return normal screen shots.
For whatever reason PB is having problems with a 64 bit Vista operating system. I still havent come up with any type of solutions to fix it. It's up to PB.