After installing or updating an ArcGIS server license you may be unable to connect to or create enterprise geodatabases and be greeted with a message along the lines of:
“The ArcGIS Server license is missing or not valid. Please provide the path to an authorization file (ECP file) that contains the server license”.
ECP files are ESRI Core Product authorization file and are created (or delivered?) during ESRI Software Authorization (see www.cryer.co.uk/file-types).
To remedy this problem, on the server where the ArcGIS Server software is installed, point the prompt at C:\Users\UserName\Desktop\License10.5\sysgen\keycodes (where the actual name of the License10.5 folder may obviously depend on the version installed.