I've been looking for a solution to this for ages: the problem that, when in Garmin Connect, if you click on the icon in the top right of the screen for "Upload or Import Activity" then try uploading a .gpx file that you've downloaded off the web or created in another application, you get the error message, "An error occurred with your upload. Please try again."
The standard solution I've found online, which works, is to connect your device (in my case a Fenix 3 HR) to a PC via the specialised USB cable (answering YES to the "Use mass storage?" prompt on the device) and copy and paste the .gpx file directly into the hidden folder called NEWFILES (under the top level GARMIN folder on the Fenix 3 HR). Once you disconnect appropriately, allow the device a few moments and then, hey presto, the .gpx file is available as a Course under Navigation.
However, there are a couple of problems with this. Firstly, you need a PC, not just a mobile phone. Secondly, you need that pesky cable with you! Thirdly, you need a PC to which you have sufficient access privileges, firstly, to reveal hidden files and folders when in Windows Explorer; secondly, to transfer files to a mass storage device connected by USB. Depending on how tight e.g. your employer is with its security (in my case appropriately tight!) one or both of these things may not be possible. Wouldn't it be great if, instead, all you needed was a mobile phone with an internet connection? (Works equally well on a PC, provided you also have your mobile phone to hand! Or indeed you can use your cable to do the final sync between Garmin Express on the PC and your device.)
So here's how to do it:
1. On your mobile phone (or PC) go to the Garmin Connect *website* (NOT the app!) and log in.
2. Click on the menu button in the top left of the screen (three horizontal lines stacked one on top of the other). Click on Training, then Courses.
3. A window appears. Towards the bottom right of it is a large blue button labelled "Create a Course". Don't click on this. Instead, click on the small blue word "Import" beneath it.
4. Click on the big blue word "Browse".
5. Find the .gpx file on your mobile phone (or PC) and select it.
6. Click on the blue box labelled "Get Started".
7. Select the course type when prompted.
8. If desired, rename by clicking on the pencil symbol to the right of the default "Untitled" title.
9. Click on the blue box labelled "Save New Course"
10. Click on "Send to Device", select your Garmin device then click "Send now".
11. Open the Garmin Connect *app* (NOT the website) on your mobile phone, switch on Bluetooth on both your phone and your Garmin device, as you usually would to sync them.
12. The Garmin device should sync automatically. If it doesn't, do it manually by going to the top level menu in your Garmin Connect mobile phone app (the three-horizontal-line one) then clicking top right of screen where you'll see an icon representing your Garmin device. Once there, click on "Sync Now". Alternatively, if only using a PC, replace steps 11 and 12 with your usual procedure for syncing your Garmin device with the Garmin Express programme on your PC.
13. Once your Garmin device has updated (you may need to disconnect from the mobile phone/PC first) you'll find you've got yourself the new Course under the Navigation section!
