I have two MBP. The '08 runs 10.7.4. The '09 is on 10.8.1 and can not work with a particular source of dmg, but the 10.7.4 laptop can. I work with an interface engine called Mirth Connect. Last night and tonight I have been trying to download a copy of the latest engine dmg. If I download it on Lion it works flawlessly. However, download the same file on Mountain Lion and the OS reports that the same dmg file "Mirth Connect Installer.app is damaged and can't be opened. You should eject the disk image." "Mirth Connect Installer.app is on the disk image mirthconnect-188.8.131.5261.b1248-macos.dmg." with the date it was downloaded. Tried putting the same file from Lion on a thumb drive and try it on ML, it chocks. The company replied to my email that "We tested it here on OSX and it works fine. The md5sum also matches. " On ML I can download dmg's from Adium, DBVisualizer and Firefox. They work fine. But these particular dmg's from Mirth Corp will not install on ML and will on Lion. Any suggestions on how I can get my dmg to install.