APU door?

From a photo displayed on the web site of Congresswoman Shelley Berkley, following her visit to the Pentagon:
http://berkley.house.gov/legis/otr/press_releases/2001/pr_2001_0913.html

Pentagon Research say:
I have speculated that it is one of the APU doors from the tail of the aircraft.

More thoughts and photos at http://www.pentagonresearch.com/074.html