I cannot sync the Garmin Swim with Garmin Express but I can with Garmin ANT+ Agent so now I have to run two applications (but not simultaneously as the ANT+ dongle goes bananas) to sync my devices.
When I go to the Garmin Swim page, it suggests that I install the latest firmware.... using the Garmin Express application! Seriously, Garmin? Don't release an application if it is still a 'work in progress'.
I am having the same problem as well. I tried to download and set up ANT+, but it won't let me sign into garmin connect. It says that is out of date and that I need Garmin Express...which of course then doesn't work with the Garmin Swim.