dmg not recognized

I'm not real sure what you are asking, so this is a guess on my part.

Select any .dmg file. Press COMMAND-I to open the Get Info window. In the Open With panel use the dropdown menu to select DiskImageMounter then click on the Change All button. If DiskImageMounter is not displayed in the dropdown menu then select Other. Navigate in the Open dialog to the /System/Library/CoreServices/ folder where you will find the application. Select then click on the Open button in the dialog.

Does this happen with files that you had already downloaded and were able to open before the update? If not, do the files have zero size? Also, please post the exact text of the message you see, or a screenshot.

Press "apple/command J" to open your downlowds window and ensure that the dmg file is completely and successfully finished. Otherwise, if the downloading is not finished and you try to open directly from your downloads directory it will prompt an error message

I followed one person's advice on another post to reset permissions, however, that didn't work. But, I read this post and clicked on the dmg on my desktop and accidentally hit CMD O instead of CMD I (as I intended to look at the Info and see if the diskmounter software was selected as the opening software), and the DMG opened right up! Hopefully, Apple will address this issue on an update soon. CMD O instead of double-clicking is not good functionality at work. BTW, afterward, I did look at the info and the diskmounter software was there.

I had same problem and i found out that when i switched of the antivirus programm and downloaded one more everything get ok. So one of the reasons could be the an antivirus.
BUT BE VERY CAREFUL FOR THIS ACTION

I had the same problem because I had reassembled split DMG files that would not fit on a single DVD. I copied the dmg.001,dmg.002 files etc from a DVD aonto my hard drive and then reassembled them with SPLIT & CONCAT - a free program for Mac.

I didn't realise that there was a second disc with extra dmg.009, dmg.010 etc files.

This resulted in a fully formed file with the correct name, but it was missing half its original content. I should have known given that such file spiltting is necessary if a file is too big to fit on a single DVD in the first place.

If you encounter the 'dmg not recognised' error, make sure all discs in the series are used to recompile the file you need.

This is happening with me also. I copied the dmgs on a thumb drive, reinstalled the Mac OS Mountain Lion and copied the dmgs back. Now they are not opening with same error message of being not recognised. All other files which were copied in the same way like pdfs and docx are working fine. It is not possible that only dmgs become corrupt.

SOlutions mentioned above dont work. 😟

1. Open your System preferences

2. Click on "Security & Privacy" shortcut.

3. Now click on the lock (on the left bottom of the window) and enter the administrator password to make changes.

4. Choose "Anywhere" and close opened window.

Now you can download and install purchased software.

If you get "Image not recognized" warning when you double tap on dmg file, it implies dmg file is corrupt or downloaded using non-supported browsers of Mac.

Fix: Re-download the dmg file using Mac supported browser preferable "Safari" without any network interruption.

I solved it! Ive tried all the things and "fixes" that I could find on the web and none of them worked... but I figured it out. It turns out that my "avast mac security", just a free virus protection software was messing up my file downloads. I turned it off temporarily, downloaded the file then bingo! Solved.

The files are corrupt. I can't say why. Usually it's a failed download.

Select a disk image file in the Finder and open the Info window. From the Open with: popup menu, select DiskImageMounter, then click Change All...