The lab service account available on this machine is not valid

If you receive the following error chances are the lab service account on the domain has either expired or is locked out. 

Here is the error you will receive on your test machines, selecting repair has no effect until the password/account issue is resolved:

Cannot connect to the controller on ‘tfs.lab.local:6901’. The lab service account available on this machine is not valid. Either the updated service account is not available on this machine or the service account is not updated on Team Foundation Server. Try to repair the testing capability and then wait several minutes. If you still observe this problem, contact your team project collection administrator.