If you get this error, it is due to App Store restrictions/security settings.  You can adjust the security settings to allow for all applications.  However, if you don't want to do that for security reasons then take the following steps:

• Hold Command and then Right Click on the install file you downloaded.  Then click Open.
  
  
   
• Then you will be asked if you are sure you want to open it.  Click Open again.
  
  
   
• The Installer should now run.