try this. I had the problem yesterday and this fixed it:
Re-register the Windows Update DLL with the commands below
Click Start, click Run, type cmd, and then click OK.
Copy and paste each of the following commands. Press ENTER after each command.
regsvr32 wuapi.dll
regsvr32 wuaueng.dll
regsvr32 wuaueng1.dll
regsvr32 wucltui.dll
regsvr32 wups.dll
regsvr32 wups2.dll
regsvr32 wuweb.dll
Then run the update again . .