unable to upgrade OS mojave to monterey

Welcome to Apple Support Communities.

Please perform this procedure:

1. First, verify that macOS Monterey is compatible with your Mac: macOS Monterey is compatible with these computers - Apple Support. If it is, continue.
2. Go to Applications (Finder > Go > Applications) and drag the "Install macOS Monterey" App to the Trash & Empty the Trash.
3. Then, Start up your Mac in safe mode - Apple Support, login, and restart back into normal mode.
4. Follow these steps again: How to upgrade to macOS Monterey - Apple Support.

Cheers,

Jack

This look like what happen if there is already an Application called " Install Monterey " sitting in the Application folder. If it exist, Drag and Drop to Trash and Empty Trash.

Try again.

Jack,

I followed all you steps, like carlomagno224 also said, but I continue to get the Checking "(null)" ... pop up.

I had previously also went back to Mojave via internet recovery.

Then I tried to update to Monterey, but got the popup.

Then another post recommended that I Cmd-R startup, and use Disk Utility to change the HD name to Macintosh HD.

Then restarted in Safe Mode, tossed the original Monterey update file, and download it again.

Still got the popup.

Then I saw your post, so I then followed your steps, but I still get it the popup.

btw - the Mac that I'm trying to update is an iMac (Retina 5K, 27-inch, 2017).

What else can I try?

Thank you,

Gino

Hi Jack, I am facing same issue but i have done this steps many times and it always show me the pop up error