Before running Cubase 5.1.2, download the latest version of the eLicenser Control Center from the Steinberg website. The version bundled with the 2009-era installer is likely obsolete and will not recognize your dongle.
Better handling of older 32-bit plugins within the environment. cubase 5.1 2 update download
: Specifically hosts the "5.1.2" revised installer for AI users. Steinberg FTP Archive Before running Cubase 5
Cubase_5.1.2_Update_PC.zip