Can't create TFS Task

I've just set up TFS2010 and connected VS2010 to it, then created a New Team Project using the default Agile template. No worries to that point. Then I tried to add a Task. It wanted a value in Title, so I supplied one, no problem there. But then it reported

The field 'Changed By' contains the value 'login-name' that is not 
in the list of supported values.

By login-name I mean the name between the single quotes is my Windows Domain login name. I can't even make a guess at a valid value, because this is not a value the user supplies. It's not even displayed on the UI.

When I try to save the Task, I get this

---------------------------
Microsoft Visual Studio
---------------------------
Save failed.

TF20015: The field 'Changed By' contains the value 'pwone' that is not 
in the list of supported values.

TF20015: The field 'Activated By' contains the value 'pwone' that is not 
in the list of supported values.
-----------开发者_运维问答----------------
OK   
---------------------------

Am I incompetent at using this? Is there some configuration I have failed to set? Help! Help! I'm being repressed!

To make things even more confusing, a day later and the whole thing mysteriously works. Neither workstation nor Sharepoint server has been rebooted to the best of my knowledge. It's all too weird for words.

Within TFS there is a job that synchronizes usernames from Active Directory to Work Item Tracking for users that have access to the server. It populates the available values for the Assigned To, Changed By and Activated By fields.

It's possible that this job had a problem or hadn't run yet, which is why it mysteriously started working again the following day.

If it happens again, you can download the Team Foundation Server 2010 Power Tools from here. Then install the Best Practices Analyzer (BPA) component and then run a health scan. It should identify what the problem is.