I have a weird situation where we have some users that we cannot assign as the owner of a task in TFS 2018. When you try to assign the user to the task, it says:
The field 'Assigned To' contains the value '<username>' that is not in the list of supported values
We've had one user that this has been an issue for for a while now. We were on TFS 2017 and I was hoping that upgrading to TFS 2018 would resolve the issue for that user, but it didn't. We have added some new users since and they worked just fine. Recently, we added a couple new users in AD (on-prem) and they get this error when you try to assign them as the owner of the task. These users are in the same AD and TFS groups as other users that do not have this issue. Initially, these new users were not assigned a license for Office 365, since they didn't need it. Assigning them a valid license didn't solve the issue though (did this because that was the only thing that was different with their accounts, compared to the other, working users). I've tried changing permissions and other stuff in TFS and have not been able to get this to work. From what I can tell we don't have any customizations that are used for these tasks. Any ideas as to what could be causing this?