Do you not have a valid Virtuoso license file in place for installation, which is require for the OpenLink License Manager service to allow continuous connections to the database. As if not then on starting the Virtuoso commercial edition it will use the Built-in Virtuoso Demo License , that runs with the indicated restrictions for about 10mins and the would start giving the license expired message requiring a restart, which sounds like the issue you are hitting. If you check the virtuoso.log file you will probably see the occurrences of the demo license being activated on startup or you have an evaluation license in place that has genuinely expired.