I have recently come across a weird issue where when we try to add / remove a UPN suffix from AD Domains and Trusts, we would get the following error.
This started happening after we patched our domain controllers in January 2022. Our PDC is at Windows 2012 R2 version.
It’s a well-known issue as per Microsoft and is due to Dot Net 4.8 so Microsoft advised to install out of band updates for the dot net version you have got on your DC. I tried that and it worked intermittently only.
I also uninstalled KB5010419 as a possible fix and again it worked intermittently only.
Apply the following reg key on all Domain controllers – Reboot. That should fix it for good.