Build machine [Machine Name] lost connectivity to message queue tfsmq://buildservicehost-1/. Reason: Please contact your administrator. There was an error contacting the server. Technical information (for administrator): HTTP code 500: System.ServiceModel.ServiceActivationExceptionResearch yielded some similar scenarios, but the configurations were too different from mine to be considered as viable solutions. Example: my build server wasn't using SSL.
I remembered reading that an update for TFS 2012 was available. Because my TFS 2012 instance is not in production use I thought that I would give the update a shot.
I apologize for the lack of tension and drama in this post, but the update resolved the issue.