Hi Dave.
This issue ocassionally pops up.
Unfortunately, because it's password related, I can't just ask people "what's your password" and discover exactly which special characters are common to making this bug appear.
What I can do is direct you to the X-Aviation password change page:
https://www.x-aviation.com/catalog/password_forgotten.php
I suggest you choose/generate something with less "special chars" in it that are likely to result in some kind of weird encoding error when they're on the way to the server.
Gizmo already uses 3rd party functions to encode the passwords before sending them to the server, but as I said, sometimes it bugs out.
Thanks,
Ben.