When attempting to log in to ArcGIS Pro with an organizational account, the following error message is returned:
Error: An unknown error has occurred. Contact your administrator to check that the license manager is running with valid licenses.
This issue occurs when incorrect ArcGIS Online or Portal for ArcGIS URLs are stored in the system registry.
To resolve the error, update and specify the correct URL address in Windows Registry Editor.
Warning: The instructions below include making changes to essential parts of the operating system. Esri recommends performing a backup of the operating system and files, including the registry, before proceeding. Esri cannot guarantee results from incorrect modifications while following these instructions. Exercise caution. Consult a qualified computer systems professional if necessary.