Task Microsoft Exchange Server Error 0x8004060c in MS Outlook

Hi guys,
The problem is with my Outlook application. I have been using Outlook to store data in PST file. However, recently I received an error message while store the same. It says, “Task 'Microsoft Exchange Server – Receiving' reported error (0x8004060C): ‘Unknown Error 0x8004060C'”. It has been running slowly and showing some other error messages. Have you any idea?
Please help me to solve the problem.
