Authentication Error with Microsoft CRM 2011 for Outlook

Hi! I am a user of Microsoft CRM 2011 I was facing an issue while connecting the MS CRM 2011 to Outlook.
The error message has been pasted as follow as a screen-shot.

Error:
Microsoft Dynamics CRM
Cannot connect to Microsoft Dynamics CRM server because we cannot authenticate your credentials.
Check your connection or contact your administrator for more help.
