Read the 'access is restricted' posting.
Various bogus attempts to register get made, which administrators will refuse.
If legitimate members want an account, they have to do their bit to distinguish their requests from bogus ones.
If an attempt isn't successful, trying again with the same username and email address as before isn't likely to work any better.
If admins don't know who a username is supposed to be, the application will probably fail.
And if a failed request is repeated with the same details it will probably fail again.
Currently, to try and curb bogus registrations from spammers and scammers, there's a question asked as part of the login process which members will either know the answer to, or can easily find out from other members.
The admins want every club member to be a forum member, and are more than happy to help people trying to join.