Disk Image fails to mount: 'not recognized'

I've downloaded the Pro Tools LE upgrade from 7.3 to 7.4, but when I try to open the .dmg file to install it, I get an error message saying that the disk image has failed to mount because it is 'not recognized'. I'm not sure that I can download it again, digidesign's website is a bit hard to navigate like that. I've tried using Toast and mount.app to mount it but neither worked. I've repaired permissions on my hard drive. I'm not sure what to do now, it just won't open. Can anyone please help?

OS 10.4 - Disk Image fails to mount: 'not recognized'

Im having the exact same problem. Can anyone help find a solution to this problem?