If you are using the ShuttlePro plug in for Mach 4 you might want to download the latest ShuttlePro software at http://forums.contourdesign.com/viewtopic.php?f=14&t=3772

When you run Mach 4 as administrator the older version of ShuttlePro software can cause problems.

I use one of the buttons on the ShuttlePro to move the Mach 4 screen between monitors (using Actual Multiple Monitors). When Mach 4 runs as administrator it does not work with older versions of ShuttlePro software. Upgraded and everything works well.