Last week a new student contacted me regarding an educational install of AutoCAD, and an odd error code that did not bring much from Google.  On first run, this error flags and shuts them down.

Unable to Initialize ADLM – Internal Error Message Error Code <21>

After some research I came up empty, except that some other folks had similar issues, but no one commented.  So I suggested the “reinstall option” and checking the user rights. 

User rights was the ticket.  Make sure your user account has sufficient rights to ADLM, file and template structures, and any the Program Data file locations.