The following error is returned when a Portal for ArcGIS Administrator attempts to assign or unassign licenses in Portal for ArcGIS.
'Unable to assign license. To proceed, you must first unassign all expired licenses for this app'.Additionally, users attempting to launch ArcGIS Pro may receive the following error:
'An unknown error has occurred. Contact your administrator to check that the license manager is running with valid licenses.'
There is an expired license for the application to which we're attempting to assign a license. For example, an attempt to assign a Spatial Analyst extension may fail due to a Business Analyst extension being expired.
Unassign the expired license in Portal for ArcGIS.