Are you trying to change your username??  If so, that would be the problem.  You can't change your username once you've settled on it.  Also, if you haven't entered your original password and the new password twice, it will not accept changes to the password. 

Right now the software is still in beta, so hopefully by the time it's finished, there'll be notifications about the error it encountered during your submission.

Does that explain it?  If not, then maybe you could change one detail at a time then hit the submit button.  If that still doesn't work, please post the exact steps of the simplest way to get it to not accept your changes.  This will help me reproduce the behavior you are getting. 

Thanks,
Chris Tuttle