How to get rid of this error? Temporary error: ymws: Server.MailboxOpenFailed?

I have been having this error for some time now. I have tried logging in different web browsers and also on my iphone and ipod but i can't see my mail

Temporary error: ymws: Server.MailboxOpenFailed

Our Engineering team is currently investigating the error on your account, and we intend to have it corrected as soon as possible. Please allow us 3-7 days to resolve this issue.