This is normally due to a permission problem on Garmin Connect. If we receive a User Permission error from Garmin when attempting to send a route we will temporarily suspend your Garmin link. You should review the connection on Garmin Connect (under Account Settings, Account Information) to ensure that permission has been given to import Courses, then you can reactivate the link from your My Settings page:
If route sending still fails to work after this, please try removing the link and reconnecting it as follows: