I hadn't used the Garmin Connect site in a couple of years. I'm retiring my old 305 in favor of a new 920XT, and wanted to upload my recent runs. The 305 has about 250 activities on it.
I normally use SportTracks to download from the watch, and that continues to work successfully with the 305. Sometimes, it gives an error when I try to download the watch, but then it succeeds on the second or third try.
I downloaded Garmin Express and installed it on my Windows 8.1 system. It has no problem with the 920XT, which has only a couple of runs on it. With the 305, it gives a "working" icon (circular spinning arrows) for a bit, then throws up a red X and says "there was an error syncing with Garmin Connect". The watch makes its normal beeps during the download, so I know they're talking. It also doesn't matter whether the 920XT is also connected.
I saw the sticky posting about the retry button being removed from Garmin Express. The only retry option now seems to be closing Garmin Express and reopening. When I do this, the sync fails again the same way. I've tried this a number of times. I haven't found a log file or any Windows events that give more details about the problem.
I went to the new Garmin Connect site (connect.garmin.com) and saw there was a "switch to classic temporarily" option. That does take me back to the site I remember from 2013. From there the "Upload" button is able to download (confusing, eh?) the 305 just fine. I've tried it 3 or 4 times so far, and no errors.
Bottom line, using classic mode resolved my problem. I'll be using the 920XT going forward. It just seems weird that the new system can't handle something the old one did with no problem. (Not sure what it's problem is, either, although there's a 787 mile activity in there which I need to review...possibly the 305 got switched on mid-flight.)
The old 305 is actually a Garmin refurb which I got a little over two years ago. It replaced my original 305, which gave me 6 years of good service. Unfortunately, the refurb literally fell apart, and the contacts connecting the two halves got damaged. I've got it working enough to download by bending a couple of the contacts and holding the two halves together with a spring clamp. If Garmin support wants to experiment on this unit, please let me know.