I don't believe that the problem is the same for your license has been purchased. It is probably your upgrade that created a snag.
Here is what you must do:
Download Key Update Tool, a utility provided by Microsoft to change the key of the Windows version installed.
The download address is http://download.microsoft.com/download/8/3/7/83712767-395c-4327-8e87-38be7b0cf75f/KeyUpdateTool_enu.exe
Double-click the utility will then check the system files.
Enter the official key and click Next.
Accept the license agreement and click Next.
The key is legalized.