I have had this problem since I got the unit a couple of years ago. I also use a 410 Forerunner. For some reason Garmin Connect will not recognize my 800 and instead it shows the 410 as the connected device. I have called support several times and they have gotten it working and then the problem comes back. Yesterday I could not upload and then this morning I could but this afternoon I can't. I am not a happy camper and I am about to give up on Garmin products. This is particularly true since tech support isn't open on the weekends and I discovered today the e-mail support isn't working (must be a Garmin product), it won't let you select the device you are asking about and it won't let the e-mail through without a device selected.
Anyone else having this problem?