I am having the same problem with my Approach G6, which I bought a couple of months ago. It ALWAYS says the device failed to synch, and I have no clue how to solve the problem. Also, it sometimes doesn't load my newest scorecards to Garmin Connect. Last time it took two or three days for my newest scorecards to appear, and this time I'm still waiting after two full days (previously, my new scorecards used to appear on Garmin Connect right away). I have emailed Garmin about these issues, and I am waiting for a reply. Fingers crossed.
The upload of the scorecards should be almost instantaneous. First log into Garmin Connect, using Modern View upload your scorecards. I would then delete them all off the device and do a master reset on the Garmin. The following FAQ provides those instructions:http://support.garmin.com/support/searchSupport/simpleCase.htm?caseId={be33bae0-f2f7-11e0-73d0-000000000000}&kbName=garmin
Once this has been completed please try to sync via Garmin Express again.