RESOLUTION
Plesk for Linux/Unix:Plesk license key is stored on the server and has appropriate record in Plesk database. It is strongly recommended to perform license key installation through Plesk administrator CP instead of moving it from one server to another. License key can be taken from Parallels key administrator system. If you do not have access to key administrator system you need to contact with your sales representative.
Generally, Plesk license key is stored in /etc/psa/psa.key file which can be transfered to the new server. Plesk CP restarting is required after the key replacement.
It is also possible to create full Plesk backup which will include Plesk data together with the license key. Further you can specify '-license' option during the backup restoration in order to restore the key. For more information please see
/PRODUCT_ROOT_D/bin/pleskrestore --help
Plesk for Windows:
Plesk license key is stored on the server in encrypted state in register. It is not possible to get license key from the server. License key can be taken from Parallels key administrator system. If you do not have access to key administrator system you need to contact with your sales representative.
It is also possible to backup license key on source server and restore it on another one. Backup/ restore procedure can be accomplished via easy-to-use GUI: Start > All Programs > Parallels > Plesk Backup/Plesk Restore ( "Backup up control panel configuration and server settings" option should be checked ) or through command line interface (CLI). For more information please refer to correspondent "Backup and Restore Utilities Administrator's Guide".