I don't know if it's alright if I join this thread - I'm having exactly the same problem as DerTroof, so I do not want to create another one. I sent a mail to firstname.lastname@example.org, but it's Sunday of course, so I'll have to wait for official reply for a bit.
I registered on Slitherine just today, and I also get the same response on the forum site, so I guess it's the same problem. I can freely browse the forum, while anonymous (except the closed forums, of course). I get "This board has no forums" message only when logged in. If I try to access a particular subforum (via bookmarks) - access is disallowed.
I am able to enter the User Control Panel - but for example I am not allowed to send or receive private messages - it's forbidden.
I already checked the cookies option (clearing them), tried Safe Mode in Firefox, IE browser access, turned off virus and firewall software for a few minutes etc. I am guessing there is some problem with forum user privileges of DerTroof and me. I tried googling "This board has no forums" and I have mostly found discussions about setting user rights in phpBB.
There is another problem for me also - maybe unconnected to the first so I'll mention it just in case. I tried playing a game of multiplayer. I issued a challenge with the DLC scenario Piatek (I copied it to the Scenarios folder). I played the first turn, the played the second and third - only to find out I was still playing the first turn - again. After this, I think my opponent got bored (can hardly blame him, I do not even know, what he saw). But I guess it might be a totally different problem with different causes.
By the way, this is my first post on either of PzC forums, so hello! :-)
Piotr 'Orlinos' Kozlowski