Hi there,
Is this an email account associated with your blog? Asked another way, is it through Google Apps? On Friday Google announced that it had discontinued that service, so that might be the issue.
Can you send me a link to the screen you're getting the error on? Or take a screenshot? It will help me to troubleshoot more effectively if I can see what you see.
Here's a bit more information about how to take a screenshot:
http://en.support.wordpress.com/make-a-screenshot/
I'm very sorry you're having this problem, I know it can be frustrating when things aren't working right. We'll get through it!