http://rog.asus.com/forum/showthread.php?9084-Rampage-IV-Extreme-00-Code-After-Shut-Down/page9

Apparently according to the VESA DisplayPort Standard (Version 1, Revision 1a January 11, 2008) the pin  number 20 must not have a wire. So the next thing on the list is testing and replacing of the displayport cables.

http://hackipedia.org/Hardware/video/connectors/DisplayPort/VESA%20DisplayPort%20Standard%20v1.1a.pdf

See page 196: