There is a known problem with some machines after SP3 is installed with inability to install updates. Here are step by step instructions to resolve 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 . .
If anyone knows someone with this problem give them this info. They will think you are very smart.
GX1