I guess I figured that because we HAVE to use the ANT to upload to Garmin Connect that it may be related.
I believe the process is ANT Agent takes the info off the device. Garmin Communicator uploads to Garmin Connect.
Garmin Communicator is used to send the data to ANT Agent from Garmin Connect. ANT Agent then sends to the device.
Therefore, best posted in an ANT Agent sub-forum for Windoze or Mac as appropriate.
In the meantime, I have seen this. My resolution was to delete the course I was trying to send from the Course folder under ANT Agent/DeviceID and resend the course. It's possible the course you are trying to send is in someway corrupted