This Problem usually occurs if the Queue-reader application is stopped or not started properly.

1. Open Windows Services and Stop “Message Queuing” service
2. In Run Command Type “%WinDir%\System32\MSMQ\Storage” and press Enter.
3. Sort(order by) the page based on ‘Type’. Then select only .MQ extension files and delete.
4. Start the “Message Queuing” service which is stopped earlier.

Make sure Queue reader application is up and running to avoid these steps in the future.