After installing the latest firmware on my 510, I can no longer use the "Send workout to device" from my phone. Using latest version of Garmin Connect for Android. A message appears saying there's an error sending workout. All other bluetooth functions seem to be working fine (i.e. uploading rides). I can also still send workouts from my PC using communicator/over usb.
I had similar issue trying to upload ride after workout. I restarted my phone, then upload ride again and it took. Sometimes though I still get the same error but just try a second time to upload via bluetooth and it takes.
