Please set both machine's logging level to Debug 1.
*Before starting with the steps, make sure that both machine's Synergy is not running (stopped)
Click Edit (on top)
Click Settings
Set Logging level to Debug1
Click OK
Restart Synergy by closing and re-opening it
* Do the same steps on both machines before trying to reconnect
Paste the log results on Pastebin or Gist then post the link here.