In ArcGIS Desktop 10.3.1 (and now ArcGIS Desktop 10.5.1 after upgrade) I have a computer were ArcMap will not start. When I attempt to start ArcMap (or ArcCatalog, ArcScene, etc.) it says 'You are not licensed for ArcGIS for Desktop Basic. Use the ArcGIS Administrator to view the software available'. When I run ArcGIS Administrator it shows I've select Basic and that I have many BASIC licenses available. Pinging the license server returns the expected IPv4 results. I've check the IPv4 connection and it is active (vs. IPv6).