Quicktime pro serial does not unlock quicktime player 7 anymore

A while ago I upgaded my Macbook from 10.5.? to 10.6.8. Since than my Quicktime Pro serial number does not unlock Quicktime player 7.6.6 anymore. It continues saying "Invalid Registration". The Apple support in Italy (where I bought both the Macbook and Quicktime Pro) were unable to answer my request.