I have installed Garmin Express (after uninstalling Ant Agent and Communicator). When trying to pair my 610 I get to the point where the watch asks me to confirm the pairing, which I do. But Express just says "Sorry, pairing could not be completed" and that I should allow syncing on the watch (!?). Meanwhile the watch has gone to a 'transferring data' screen which stays up for a couple of minutes.
I've gone around this merry go round a few times now. I'm giving up and am going back to Ant Agent. Don't know why they had to "fix" what wasn't actually broken.