Often times when get things that are mixed up like that, the easiest thing for me to do is remove them from the MDM, uncheck them in pre-stage and re-image.  This usually gets me back to a place where the machine works normally, albeit with no MDM.  Then I can add it back to the prestige and re-image a second time and it usually picks things up properly.  Sometimes I do this on 6 or 8 Macs per week, so it’s not uncommon for me.  I’m sure there’s a more appropriate work around, but I often haven’t got time to sit down and sort through it.

Is your MDM profile removable or nonremoveable?

Is Jamf still able to send MDM commands to the iMac? Then you should be able to use the "Remove MDM Profile" command from Jamf. 

That's a better answer than my "wipe and reload" solution.  😊

Follow this guide on how to remove a locked MDM. Look at the steps further down which requires you to boot to recovery mode to do this. This has always worked for me.

You're thinking of this one, right?

http://www.whoopis.com/core/mac-related/removing-a-non-removable.html

It will fix a non-removeable profile. If it's removeable you can just delete the MDM profile under System Preferences > Profiles.

Yes, that's it. I can't believe I forgot to include the link. 

http://www.whoopis.com/core/mac-related/removing-a-non-removable.html

Yes! This works for me!

:( that didn't work....
Computer is not in JAMF Console anymore and his Profiles are greyed in sys preference and cannot re-enroll because profiles is blocked...

This is indeed a tricky issue. But don’t worry. I have a good tool named Joyoshare iPasscode Unlocker suitable for you. It’s the best way to help you remove the non-removable MDM profile with a high success rate. Even if you don’t know the account and passcode. It’s worth emphasizing that your data will not be lost. You can use it with peace of mind. It is compatible with all models of iOS devices and versions. Now you can refer to specific steps about how to remove non-removable MDM profile.