All of a sudden my Garmin Edge 500 stopped syncing my data correctly with the Garmin Connect Servers. I forget the exact problem because so much water has passed under the bridge by now. However I think it would say it had synced correctly but no data actually appeared in my account.
My first attempt to resolve the problem after a couple of frustrating days was to uninstall all the Garmin software, reboot the PC and then reinstall everything at the latest levels. The problem then changed! The install appeared to go correctly but each time I tried to start Garmin Express it would come up with a message saying "Device found", then fail to show the serial number, and then say there was a problem connecting with the Garmin servers. As you all know there have been multitudes of problems about connecting to the Garmin Servers - you could go away with the impression that the Garmin Servers hardly ever work given the volume of messages about those problems. So I played around for a few days thinking this was an unfortunate coincidence. Then I got a bit more desperate and decided to contact Garmin Support via email. This was (and is still) a dreadful experience - truly dreadful. In the first instance responses take ages (four or more days), in the second instance they respond with formulaic and ridiculous scripted responses. I was told it could be a firewall (I have never, never, ever had a problem with firewall access - this is one of those long standing c0omputer myths). Then I was told the resolution of my screen display could be a problem and I should have 1024 x 960 or something - totally ridiculous! - there can be no such connection! Then I sent them screen shots, copies of their diagnostic logs etc and I'm still waiting for feedback 5 days later.
Now over the year or so I have had the device it has had a tendency to suffer from what Windows describes as "errors on the disk" i.e. Windows has some reason to believe the usb drive within the device is a bit dodgy. Occasionally Windows confesses that it has found a problem and corrected it, but more often than not it says no errors found and everything seems normal - there still remains the fact that Windows was somehow alerted to a possible problem and Windows does not tend to do this with the many other usb drives I use, which perhaps means the Garmin storage is a bit suspect in terms of quality.
Leaving that aside for a minute I'm a little bit of a computer nerd and so every now and again I switch on the option to view hidden and operating system files - then I tend to see a load of FOUNDxxx files on the Garmin device - these files are created as a result of the Windows recovery actions when it does find problems with the device - i.e. it finds sectors on the device which are not correctly tied into a chain of sectors which make up a file!!! Now unfortunately Windows says it has corrected these problems when it has created the FOUNDxxx file - however it has not corrected the problem in the way that you and I would understand the term i.e. it has not re-associated the orphan sector(s) with their original file, but merely given them a new file name (FOUNDxxx) and placed them back into the disk structure as a new entity - you will have lost data - this may or may not matter depending on what the data was!! I had been aware of these issues for a while but up to now they had not caused me any problem, so I had ignored them.
So given I was getting nowhere with Garmin Support I looked at the device and after a while decided the files that really mattered were the *.fit files in the S:\Garmin\Activities directory. A new one of these files is created for every activity (cycle trip in my case). So I copied the files that had not been uploaded, to another disk drive - these files are easily identified because their names are the date and time of the activity. I then did a master reset of the Garmin Edge 500 - this effectively wipes out everything and reinstalls the basic software on the device having recreated the disk structure. You have to go through the process of choosing device options (language etc) and then when you connect it to your PC - BINGO! It all works. So the problem was almost certainly one of those disk errors whereby a portion of an important file "went missing" - in my case the device had been acting a bit funny shortly previous to this "dead in the water" situation when it kept downloading the same update time and time again, but I had assumed this was a Garmin Connect issue (the device did however continue to work perfectly normally when out on a ride and recorded al;l the data one would expect!). The only thing that remained now was for me to copy the files *.fit files that I had backed up back into the S:\Garmin|Activities directory and then connect the device up to Garmin Connect again - it uploaded my "missing" data and I'm back where I wanted to be.
It just a shame Garmin couldn't have told me this and I had to work it out for myself over 2 weeks - I would imagine quite a lot of other "Garmin Express" connect errors are due to the same problem. Your mileage may vary! Good luck.