OS X El Capitan suddenly can't open DMG files I am trying to open a DMG file to install an OS X app. I get the error The following disk images couldn't be opened. Invalid Argument. I have tried to open other DMGs that I successfully managed to mount earlier and they are failing too. So the issue is not with the current DMG only. I restarted and that did not make a difference. I ran First Aid in DiskUtility and it reported that my drive was corrupt and needed repairing. I therefore restarted my mac with cmd + r pressed, selected Disk Utility and ran the repair. The repair failed after running for about 5 minutes. I would like to keep the contents of the drive if a solution exists that allows. What should I do now?

UPDATE:

I did a time machine backup and let the iMac go get its drive formatted etc. I then attained a macbook air, and did a Restore From Time Machine onto it such that I have back where I left of on the iMac. I then tried to open a new DMG, and the same error came up. I ran First Aid on the mac air drive and it reported it to fine (Ran Successfully).

This is therefore not a drive issue right (first aid on the mac air succeeded)? What could it be, and how can I fix it.
I had the same problem, and managed to open .dmg files by going into Disk Utility>File>Open Disk Image. Once opened in Disk Utility, Double Click (Right Click) the icon and click show in Finder. Then I could install what I wanted! Hop it works for you!