That was a relatively common cache problem in the past. 

Open your explorer and navigate to C:\Documents and Settings\All Users\Application Data\Stardock\Impulse\backup. 

There should be a bunch of files there with .impulse extensions.  Move everything out of that folder to a safe backup folder and try downloading and archiving again. 

If it works, you can delete the stuff you moved out.  If not, you haven't lost anything and can move it all back.

I thought the cache problem had been resolved a while back.  After clearing the cache, you might want to double check to see if you have the latest version.

Are you using Stardock TotalGaming.Net application or Impulse?

Reason I ask is: I couldn't update with the TGDN application (through which I originally bought these games) but when I downloaded, installed and ran Impulse, the updates worked.

If this problem is still occurring, please contact support@stardock.com about it.

Checking against what you have tried already I would have to think that you have some sort of corupted data from the download. Have you cleared the downloaded files yet and attempted the full download again? If not please give it a try and be certain to restart the machine between deleting and the new download.