Usually a restart of the TDoD service resolves this issue.
If you are not able to restart the service, first launch Datamaker and connect to the repository database. Once the connection is complete, try to restart the service again. You should be able to start TDoD now since the connection to the repository database, and license that is held there, has been established for TDoD.
If the TDoD service is not able to access the back-end database, the service (by default) will shut down, and this is by design. However, since TDoD is implemented as a Windows service, you can make a change to the service itself to restart the service if it goes down. Below is a link that talks about setting this up if needed- https://serverfault.com/questions/48600/how-can-i-automatically-restart-a-windows-service-if-it-crashes