The Blizzard Battle.net desktop app doesn't have permission to read from the selected folder and it can't check for your game installation there.
Disable or temporarily uninstall any security programs, which may mistakenly identify the login module as a security threat.
If you're trying to connect from a public network such as a school, hotel, or office, contact the network administrator to make sure their proxy is set up properly.
If the problem persists, uninstall and reinstall the game.
Try moving files to the Applications directory to allow the application to run with full permissions.