If you bought from the web, and not from inside flight sim, you should use the "Register Serial", NOT the "Reinstall" function.
And, anyway, the "Reinstall" function should be only used as a backup, in case you lost your serial, or you don't want to type it. The preferred, suggested, and better method is, as clearly suggested in the forum topic I've sent you, is to use the "Register Serial" option.