This issue can occur if (a) the file contains a Desktop Color Separation (DCS) picture that includes multiple color plates, and (b) one of those plates' colors is unchecked in the Color pane of the Print dialog box (File > Print).
- Open the project in QuarkXPress with the QuarkDispatch XT loaded.
- Choose File > Print.
- Click Color in the list on the left.
- Check the plate in question, click Capture Settings, and resave the project.