Yes, that's the URL I'm using exactly.
Agreed, users will normally login via the forums and so bypass the problem. There are 2 specific exceptions that I'm trying to deal with, though:
1) If one member shares a PP link with another (say to a specific photo), then, unless they happen to be logged into the forum already, they will be directed to the login screen (since the forum requires Registration), and this login is routed from PP, and hence the user gets the Internal Server error.
2) I would like to access the Admin panel without going through the steps of logging into the forum, clicking on Photos in the VB3 navbar, then clicking on Admin on the PP navbar. Although, I can definitely live without this one...
so, it's really 1) above that I need a solution (or workaround!) for.