Some users were unable to install the Synergy 3.5a release made available a couple of hours ago. If you are one of these users, please download the updated version (3.5a2) which is now on the servers.
You can download the updated release from here and purchase a license using this page. The 3.2-series can still be downloaded from here. This is a free upgrade for users who already hold a valid Synergy license.