Basically, if you are an active customer of this application, you will have to contact the developers, because they have the power to check the status of a serial number/activation key. The only thing I would recommend is reinstalling the application, because in most cases, when you try to activate the key in another installation, it will disable the other one. But there are chances that the key can be used only once or twice then it expires or becomes invalid.
Use the following support page to contact the developers: http://www.wingsinfo.net/network/
Note: Choose a representative that's close to your location to make it easier to diagnose the problem.
