The product key isn't recognized for long.
Press the Windows key and "R" at the same time. A "Run" dialog box will pop up, please paste the path below into the "Open" field and press OK.
In the folder that pops up, you should see a folder named DeskScapes. Please delete this folder and all of its contents.
After you have deleted that folder, please attempt to activate once again and it should succeed without any errors.
Stardock Support Manager