Used synergy 1.3.1 & 1.3.4 since 2007 without a hitch. Upgraded to Windows 7, and synergy suddenly stopped connecting after a week. Now any version I try (1.3.1, 1.3.4, 1.3.8, 1.4.5) goes into high CPU usage, no TCP connection makes it through, synergys process uses "Realtime" priority on install. Windows Firewall is open. Tried removing ipv6. Only way to get a TCP connection to go through is to enable "XP SP3 compatibility mode" and "Run as Administrator"... although that's not enough to get keyboard/mouse sharing to work.
Make sure scroll lock is not active! I had a similar problem and ended up here (though the connection was working), deactivating scroll lock solved it! https://code.google.com/p/synergy-plus/issues/detail?id=217