This is a Mac OSX security issue. To fix the problem:

  1. In System Preferences select the ‘Security & Privacy’ panel.
  2. If the panel is locked click the padlock icon in the lower left corner to make changes.
  3. In the ‘Allow applications downloaded from:’ section select the ‘Anywhere’ button.

You can change this preference back after you’ve installed and run Vista v2 at least once.