Update 5608 won't update

I've tried a number of times to update to build 5608 but it won't do it. It downloads the update and then it ask if I want to run the installer, then nothing happens. If you try and open the .dmg file that was downloaded to my desktop it claims that the disk image didn't mount properly. Any suggestions? Thanks

 

download build 5608 following link bellow:
http://download.parallels.com/v3/en/GA/Parallels-Desktop-5608-Mac-en.dmg

and reinstall Parallels Desktop as described in kb
http://kb.parallels.com/en/4790