Protected content register ends in an error

I have a form (application) that after they fill out goes to register
http://www.kingscountyradioclub.com/register/
then they pick the plan and errors out the url it ends up at (don't know if it maters but including it here anyway) goes to
http://www.kingscountyradioclub.com/register/?action=register_user
and errors with this
ERRORERROR: Domain not allowed.