Error showing whenever I receive an Email in Outlook for MAC 2011

Hi Everybody,
I’m in need of someone to help me in this matter.
I’m getting this Error Message (below), whenever I receive an Email in Outlook for MAC 2011.

Mail could not be received at this time.
The server for account — • returned the error "authentication failed". Your username/password or security settings may be incorrect. Would you like to try re-entering your password?
No Yes
May be I didn’t enter a correct setting. Please help me to resolve this issue.
Thanks. Have a nice day.
