Same problem here.
first my pc couldn't identify the usb driver. After changing the cable it was possible to re-install the driver and connect the device to Garmin connect but the course couldn't be uploaded to Garmin Connect and the same error code appears: There was an error syncing with Garmin connect. :(
Same issue in all browsers as well. I assume this is a known issue across all users for Garmin but I can't find any statements about it. Hopefully it will be resolved soon.