High CPU usage for QuarkXPress Server subrenderer process

1. Shut down the QuarkXPress Server application.
2. Browse to the 'XTensions' folder in the QXPS application folder.
3. Move the 'Vista.xnt' and 'OPI.xnt' files to the 'XTensions Disabled' folder.
4. Re-launch QuarkXPress Server.

Brief description of these XTensions:
Vista XTensions software is used to apply and remove preset files containing QuarkVista effects to pictures in picture boxes before rendering a project.

OPI XTensions software provides enhancements to the Open Prepress Interface (OPI) features that are built into the application. In an OPI system, you work with low-resolution versions of pictures, and then the high-resolution version is replaced by the OPI server at output.