This problem appears to be caused by Installshield.  To resolve this problem, please do the following -
  1. Open up My Computer
  2. Navigate to: C:\Program Files\Common Files
  3. Cut out the Installshield folder and paste into temporary location.
  4. Install Stronghold 2 as normal. You may want to try running the Setup.exe directly from the CD/DVD.
  5. After the game is installed. Paste the Installshield folder back into: C:\Program Files\Common Files
  6. Also clear out the Windows temp folder. Usually located under: C:\Windows\Temp