Important: Before you do anything else, please open a support ticket.
Sometimes the background service can get into a bad state. This is most commonly caused by either sleep/resume, a change in IP address, or just random bad luck, but other factors can affect it as well. This is a known bug and we're urgently working on a fix for this problem.
In the meantime, please could you open the Synergy config app and press the key combination Shift+F5 on both computers. This will r