It seems like you had installed an older version,
Please make sure that you are using version 2.1.1.1
(the product key activation will not work with any older version)
We had to change the way we generate product keys,
Please download the latest version (2.1.1.1) of Screen Mode Switch
and activate it, you can manage your account at The My Account Page
You can also update your software by right clicking the Screen Mode
Switch icon at the tray as follows:
http://MicroMighty.com/Temp/SMSwitch/UpdateScreenshot.jpg