Hi,

If you connect the dongle to you mac with the USB cable and run this command in the console: system_profiler SPUSBDataType

Do you then get something like this in the result?

        mcBoot:

          Product ID: 0x6015
          Vendor ID: 0x0403  (Future Technology Devices International Limited)
          Version: 10.00
          Serial Number: MC8AAAA
          Speed: Up to 12 Mb/sec
          Manufacturer: FTDI
          Location ID: 0x14100000 / 5
          Current Available (mA): 1000
          Current Required (mA): 90
          Extra Operating Current (mA): 0



If not then I think you need to install the ftdi drivers for OS X.  If the OS X does not find the device I don't  think you can map it into the Virtualbox.