[TFS] Object is already checked out to . (empty user)

This morning I wanted to check out an object within Dynamics AX 2012 which is connected to a local TFS instance. The system came up with the following error message:

'\Forms\CustSettlement' is already checked out to .

error log screenshot

After checking it withing source control explorer from Visual Studio, the object is not locked by anyone on the server. That means the TFS server does not know about any locks on this object which leads me to the fact that something within AX must be the cause.

After checking my infolog again, I noticed another message at the top:

The file 'C:\TFSPublicWorkspace\DEV1\Main\SOH\Forms\CustSettlement.xpo' was not correctly imported to the model store in a previous synchronisation. Any updates of the file is blocked from AX. Open Version Control, Synchronization log to re-import the file.

The solution was to check the Version Control Synchronization log as suggested by the message and process the unfinished entries again.
To do so, open the log under Version Control>Synchronization log, click on the button Clean up log and then use the button Process to import the unfinished objects again.

After that, the misleading lock message was gone.