Windows Defender Error with Windows 7

Hi,
I have recently installed Windows 7 on my system and I am using Microsoft security essentials (MSE) as my antivirus. When I open my windows security, the windows defender is switched off there. When I click on it, an error pops up on the window. The screenshot of the error is as follows:
Windows Defender
Windows Defender encountered an error: 0x800705b4. This operation
returned because the timeout period expired.
OK
After getting this error message the lower part of the windows security starts flashing showing the ON and OFF switches.
Can anybody be of some help for me? I am already using MSE as an antivirus. Even then do I really need my windows defender to be in working order? If yes, then please guide me how can I make it work?
Looking forward to your replies.
Best Regards.
Ron.
