Often, user names are not allowed because someone else is using them. It may also be a case of keeping the confusion down. The name "Kings-Pawn" in the middle of a posting might create soe confusion. Try contacting the adminisrators if you have questions about this...
Great Website, Just a few questions

I think there is some filter that checks for similar user names:
http://www.chess.com/members/view/KingsBishop
http://www.chess.com/members/view/KingsKnight
http://www.chess.com/members/view/Kingspawn
Hello there, my name is John and I have just joined chess.com (Excellent website by the way)
However, I do have a few questions. When I first joined, I was thinking of a few user names that I would like but they are not allowed. Why is that? Here is what I wanted.
But I got an error message stating that my user name was not allowed. I can understand the first one as it may seem too, "Official" but the last three I cannot understand.
Anyway, I should be required to change my user name, I will do so willingly.
Thanks,
John