The board, by default, was adding newly registered user to the "Newly Registered Users" group. (Logical I guess).
Also by default, a user remained in the group until a they had made 3 or more posts on the forum
Also, Newly Registered Users" were disabled from sending using the PM (Private Message) system although they could receive PM's.
As we are not using the forum and therefore no one was posting you were always going to remain newly registered and therefore not able to send PM's.
I was not aware of this restriction until I looked. Everyone has now been removed from the "Newly Registered Users" Group and this feature has been disabled. So every one should be able to PM anyone else.
I've also enabled you to forward PM's and allowed you to use BC Code to pretty up your PM's.