You Have to choose Serial, the USB option is not for your Adapter ( it is for the next Generation of the EMS Series).
First plug in your USB to Serial adapter and install the driver which was coming with the adapter.
After that, check in the Computers Hardware settings what COM PORT relates to that adapter ( should be one at Com 1 up to 16, you will see the Adapters Name beside that Port )
Then start AEM Pro, choose serial port and the Com Port in the pull down window which relates to your USB Adapter.
Then choose connect.... it should work now.
OH, by the way: Plug the USB Adapter EVERYTIME in the same USB port, because using an different one will change the Serial Port Number ( on most of the USD to Serial adapters )
He's absolutely right.....
http://forum.aempower.com/forum/index.php/topic,21870.0.html