1) Where did you purchase your copy of Windows 7 from? Did you activate online?
Ever since MS released WAT (Kb971033), there have been many cases of genuine windows being flagged non genuine. That may be the cause in your case. The solution is to call MS.
OTOH, if your copy is non genuine, WAT may have detected it now either because that update has been downloaded recently or because WAT's signatures have been updated by MS to catch the particular activation hack your computer may be using.
You can check on the MS site ("How to tell"), whether your Windows 7 disk is genuine or counterfeit.
2) Download and run the MS Diagnostics tool. http://go.microsoft.com/fwlink/?linkid=52012
Click on the Copy button to copy the results to notepad and save that as a text file. Upload the file here. That may help.