If you see the following error message in your connection log:
Tue Sep 1 22:17:22 2015 MANAGEMENT: Socket bind failed on local address 127.0.0.1:1337: Address already in use
It is likely that the port needed for the connection attempt to the server location is not responding or is being used by another process. To solve the issue:
Restart your machine. After that, launch ExpressVPN again and connect to a server location.
Troubleshooting
If you are still encountering issues, connect to a different server location. If the problem persists, restart your machine before reconnecting to ExpressVPN.