Each machine running the ArcGIS Server Object Container requires an ArcGIS authorization file. There are several ways to register ArcGIS Server. You can visit http://service.esri.com to obtain an authorization file (by email, fax, phone or mail) before installing ArcGIS Server. You can also register ArcGIS Server using the setup program. See the Authorizing ArcGIS Server section of Performing a typical installation for more information. The authorization tool can also be launched using the authorization script from <ArcGIS Server installation location>/arcgis/scripts/authorizeSoftware
Registration requires the registration numbers (similar in format to ABC123456789) provided by Customer Service. Visit http://service.esri.com for more information.
Each new version of ArcGIS Server requires a new authorization file.