“That account name is not allowed for use with this service.” in Windows Live Admin Center

Halo,

I have experienced an error message when attempt to adding a new email account via the Windows Live Admin Center. 

The error message is "That account name is not allowed for use with this service.", when I try to create "winnie" as an account name.

I have tried to create other accounts and all passed, except "winnie", could you please assist me to resolve this problem, because this account is for work purposes, so I look forward to your feedback as soon as possible.

Please let me know if you require any further information.  I would be appreciated if this problem can be resolved or escalated.

Thank you in advance.

Geo