I had the same thing and in the end I sent an email directly to the forum somehow, can't remember (not much help!!), but I got an email back to say that it had been manually registered. Initially I got a welcome message with a confirmation of my log in etc, but then it said that the application would be reviewed and that I would be sent another email to confirm, and then I would be able to log in. However, the 2nd email never happened. Think I tried twice before emailing direct.
Have got the same problem with the 4paws forum - have registered so that I can take part in the photo competition, have received a confirmation, but no acceptance email.