Does the device go into USB mass-storage mode (silver computer icon)/MTP mode (amber/orange computer icon) when connected to either computer? Macs do not support MTP mode and when connected the device should show the silver icon and when connected to the Win 7 computer it should show the amber icon. Disconnect the mount from the device and ensure you are connecting the USB cable to the device and not the mount.
If that is not the issue, have you tried the troubleshooting in our FAQs?
Why is my Garmin mass storage device not communicating with Garmin Mac applications?
Why is my Garmin mass storage or MTP device not communicating with Garmin Windows applications?
If the issue persists, it would be best to contact Product Support by phone for further assistance.
The device does go into USB mass-storage mode and MTP mode depending if I plug it into my mac or W7 machine. I can even see the internal memory and SD card appear as extra drives. they are both empty apart from an ID file...not sure if this is the problem.