The message indicates you are trying to install an upgrade version of this software and it is asking you to choose the older qualifying version that you already owned and to enter its serial number... for CS6 this would be CS5.5 or CS5.
Error "This serial number is not for a qualifying product" | CS6, CS5.5, CS5
http://helpx.adobe.com/creative-suite/kb/error-serial-number-qualifying-product.html