Win 7 64
I was having the USB connectivity issue where I could access the SD card but could not connect to the printer due to an error loading the USB driver.
As a test I reinstalled MatterControl, which I had been using prior to getting the smoothie card, in the install process MatterControl installed a USB driver from MatterHackers and lo an behold, the USB driver installed correctly and Pronterface can now see, and control the printer via USB.
Imported from wikidot