Maybe the eMagin connection is timing out?
Might try installing eMagin's Lab Tool available here:
http://www.3dvisor.com/support.php
and turn off or mazimize the timeout settings.
This tool is pritty handy for other emagin stuff. But don't think you can't run it while connected to the eMagin tracker with Vizard.
Then again, the drift on the eMagin tracker is so bad its really only useful for relative gesture recognition.