Calibre cannot communicate with Kindle Oasis.

I've read through some of the other threads with the same issue, but nothing has helped me solve this problem... here is the error message I get -

calibre, version 4.21.0
ERROR: Error: Error communicating with device

Failed to access files in the main memory of your device. You should contact the device manufacturer for support. Common fixes are: try a different USB cable/USB port on your computer. If you device has a "Reset to factory defaults" type of setting somewhere, use it. Underlying error: [Errno 1] Operation not permitted: u'/Volumes/Kindle/driveinfo.calibre'

Traceback (most recent call last):
File "site-packages/calibre/gui2/device.py", line 90, in run
File "site-packages/calibre/gui2/device.py", line 473, in _get_device_information
File "site-packages/calibre/devices/usbms/driver.py", line 163, in get_device_information
IOError: Failed to access files in the main memory of your device. You should contact the device manufacturer for support. Common fixes are: try a different USB cable/USB port on your computer. If you device has a "Reset to factory defaults" type of setting somewhere, use it. Underlying error: [Errno 1] Operation not permitted: u'/Volumes/Kindle/driveinfo.calibre'

Any help would be greatly appreciated.