Please go through all the marked pins in this post: USB Device Not Recognised - #5 by Giedrius - you have to make sure the contact and soldering is very good for those, as they are essential for the USB to function properly. Some people also find success if they place a USB hub in between the Midiboy and the host computer, or a different USB cable length. As the USB is emulated in the microcontroller’s software, it can be a little sensitive to the physical configuration.