There has been a bug in the NC download application for a while now - if the email the server sent failed to go, then it was just lost. I fixed that this morning - the server is now logging such errors, and running a background process to attempt resends. That should clear up one of the bigger issues with the download application. There's another issue with bad error messages, which I intend to take a look at this afternoon. Thanks for your patience!
Update: - as it turns out, one of the larger issues was error reporting - the application would tell the end user "username is already in use" regardless of why the username was invalid - very confusing, and a big error on my part. I've fixed that, so the application should be clearer about issues now.