Which version are you using, full number is to be found under Help, About Captivate.
Do you publish to HTML5 only? Can you check if the Publish folder (Preferences, General Settings) is really on your system, not on a netwoked drie? If you are on Windows, do you run Captivate with 'Run as Administrator' setup?
You talk about Preview, which Preview mehtods? Is this a non-responsive or a Fluid Boxes porject?