I purchased a DraftSight Standard and installed on a pc. The CAD tech was not able to do certain things to I purchased another license but this time I purchased the Professional. He can now do more advanced things.

Now I have a manager that just needs to view these drawings, so I installed the available Draftsight Standard license to his pc but it provides an error stating that it has already in use. I know that I fully uninstalled that Standard license on the CAD tech's pc, and all it shows is Professional version. Why can't I install the available Standard that I paid for on the manager's pc?