It seems that Encore does not run on Mavericks. Im trying to sort out the issue myself and there arent many options.
Gary, from another post, you are trying to run EN CS5.1 (i.e Encore for CS5.5)? Are you getting this "nonserialized" message, or just a crash?
Other users appear to get EN CS6 to open on Mavericks, and have other issues.