If you changed any kind of the hardware in your system, or tried to install DSS on a different system, and you have an old Activation file, it will not work, as you need to get a new Activation file for Offline activation, or else you can activate it online.
More details can be found at this KB:
http://kb.open-e.com/How-to-activate...oduct_702.html
Please send us a new .HWS (hardware stamp) file for your system, and we will generate a new Activation file for you, you can open a support ticket for that, or just send the HWS file to the mentioned email in the KB.