GPS Data Logger Software - BT747

I have a QStarz 818 connnected via Bluetooth to BT747 on an iMac running Mavericks.(I can also connect via usb with no difference to the outcome described below) The gps unit connects with no problem and I can see the GPS Device Data in realtime. However when i click "download" nothing happens and there is no progress in the 'download progress' box at the bottom of the screen. I can upload AGPS data to the device. I feel I am missing something really obvious, but I cant figure out what that is. Can anyone please shed some light on what I am doing wrong? Thanks :-)