Add New Users Plugin- Errors and Freezing

When you try adding a new user through the Add New User screen it will either give you an error: "Only characters A-Z allowed", and/or it will freeze on that screen and you have to click "stop" on your browser or it looks like the page just keeps trying to reload.

The user is actually still being added regardless of the errors, but I need to get this functioning properly for the client. Thank you!