Garmin connect said that it now uses Garmin Express.
"Previously your device talked to Garmin Connect or your computer using the Garmin Communicator Plugin
or the Garmin ANT Agent. Both have been replaced by the new Garmin Express program."
it then take you to the download page for a install of Garmin Express, but I already have it installed, so I installed it again. then restarted.
Reopened Garmin Connect to upload the course again and again back to the same message and same download page.
Garmin connect is not seeing the installed programe (Garmin Express). Garmin Express sees the 510.