I can't update any MacOS software on my iMac.

System installers that do not finish end up in the Applications folder. Other updaters use the Downloads folder for depositing their disk image containing the update app.

I've had better luck installing system updates from the Safe Mode because I evidently have some 3rd party software that interferes with the installation so try the following:

#1 - boot into Safe Mode according to Start up your Mac in safe mode - Apple Support.

NOTE: Safe Mode boot can take up to 3-5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

#2 - go to the System/Software Update preference pane and begin the download.

#3 - run the installer from the Safe Mode.

It is really important to our effectively helping with OS compatibility questions for you to tell us the SUB-Model of the iMac and the macOS version it is currently running. Both are quickly available from "About this Mac..." under your Apple menu:

OS compatibility solely depends on that sub-model. and any upgrade path depends on you current macOS. At some points, a mac becomes too old to support the latest OS versions.

Otherwise we are guessing and that seldom has a good outcome!

jimwalsh1964 wrote:

: This copy of the Install macOS Monterey application is damaged, and can‘t be used to install macOS.

The copy of the installer on your Mac is old and was signed with a certificate that is no longer valid.

Delete the installer, empty the trash, reboot, then re-download it from the App Store.

Perfect

Then the message about "damaged" that Kilted Tim points out is spot-on.

Do you realize that when you leave Mojave, older version of software like Office 2011 and older, or older version of Adobe Creative Suite will not work? All apps must be 64-bit once you leave Mojave. This free tool helps you check your current apps' status:

https://www.stclairsoft.com/Go64/

IF there are apps you absolutely need that cannot be updated to 64-bit by the developer, you may wish to wait to upgrade.

That is what Tim mentions. That means the installer found an older, deactivated version of itself in your Applications folder. Delete it and try again.

Are you using Safari for the download? If not, try that as well. A few months ago people were having issues if they tried to do the macOS download and install with FireFox. Although it is said to have been fixed, Apple articles on getting OS software still recommends Safari the last time I looked.

I have exactly the same error message, and I've noticed quite a few posts in various forums from others with the same error.

I've tried deleting the Monterey install package (as well as deleting it from the Trash folder) and downloading a fresh copy, also tried de-activating my Norton anti-virus, and tried installing Monterey in Safe mode - none of these work and I get the same error message every time.

I have a 2019 MacBook Pro 13 inch, running Mojave 10.14.6 with 8GB memory and Intel Iris Plus graphics. When I check for updates under System Preferences, Monterey is the only update/upgrade offered.

Thanks in advance for any help!

Problem solved - I was able to upgrade Mojave to Catalina, and then Catalina to Monterey, with no problem. For some reason (I don't think it has anything to do with Norton) I was not able to upgrade directly from Mojave to Monterey.

What happens when you try to update your software? Does it not find an available update? Does it start the update and it can't complete it? Do you get an error message? Let us know.

Paul