So, after reading the forum, I see many other users are facing similar issues with other devices. I am running latest software on Mac (Yosemite 10.10.3), on Garmin 920XT (4.20) and on Express (4.0.24.0).
HELP
I am sorry that you are having trouble with Express. We are seeing this issue when trying to add devices using computers that are set to certain region formats. We are working to correct this issue but in the meantime, you may be able to add your device to Express by following these instructions:
Click the Apple icon
Click System Preferences
Click Language & Region
Change the Region to United States under Americas (Other regions will work as well but I know this one will work)