I’ve been using Garmin Connect for several months; firstly with the Garmin Fit iPhone app and later with a Garmin Edge 500. I have been logging in to Garmin Connect and connecting the 500 by USB for upload. And then repeat to upload to Strava. (The 510 and 810 can connect by wi-fi to a phone and upload from there.)
Garmin recently updated the Connect website with spiffy, new features and a clean, new look. However, it thought best to remove the upload button, apparently to reclaim valuable screen space. To upload (or sync) to the Modern Garmin Connect, one must install the Garmin Express application. Since Garmin Express works for my Nüvi navi and handles syncing and software updates in one place, it seemed reasonable to use instead of the old MyGarmin dashboard.
But the 500 worked once with Garmin Express, syncing to both Connect and Strava.
The next time I tried Garmin Express, the time zone software update appeared for installation, even though I had installed it the old-fashioned way with MyGarmin after it had failed. Sync failures would be explained as the PC not finding an ANT+ adapter, which is applicable to the Forerunner range. Since the 500 was connected by USB, an ANT+ Adapter is irrelevant.
The workaround was to temporarily revert Garmin Connect to its ‘classic’ view with upload button. But the classic view won’t last forever.
Was the Garmin Communicator browser plug-in clashing with Garmin Express, as some forums suggested?
The solution came by installing the ANT Agent from Garmin, which made Garmin Express happy. The ANT Agent will display a warning that it can’t find the ANT adapter. Ignore this error, since now your Garmin Edge 500 (or other device connected by USB) will be recognised. Possibly.
Syncing from Garmin Express will upload to Garmin, just as nature intended.
I hope that helps. I hope it works.
UPDATE: July 2015
Forget all of that. Uninstall Garmin ANT Agent and any other Garmin plugins and whatnot. The latest versions work. Since a few updates ago, the Garmin Connect and Garmin Express combination appear to be working according to spec. Sometimes it takes its time to recognise my 500, sometimes it forgets to auto-upload to Strava and sometimes it auto-uploading everything twice, but it is working.
I have Garmin Communicator Plugin 32-bit and x64 v4.1.0, Garmin Express 22.214.171.124 and Garmin USB Drivers v 126.96.36.199 (to support a Garmin USB ANT+ adapter).