from the post:
my loose working hypothesis is that some 'faction' decided to take the rumours that saddam had once considered mobile weapons labs and they ran with it. The hypothesis is that Chalabi, financed by Rumsfeld, decided to leverage that original story by planting a source (Curveball) who claimed that he was involved in the manufacture of these labs. Contemporaneously, Rumsfeld et al organized the manufacture of more than one of these labs - utilizing the expertise of Stephen Hatfill. I also posit that one of these labs-on-wheels was supposed to be planted in iraq as 'proof' of saddam's WMD capabilities and intentions.
For one reason or other, this endeavour failed. I'm not sure if it's because David Kelly decided not to play along, or if Brewster Jennings discovered the plot, or if something else happened. What is apparent, though, is that the administration decided to desperately stick to the original script regardless of the facts on the ground - with Bush demanding that he had found Weapons of Mass Destruction.
here's the timeline
http://wotisitgood4.blogspot.com/2006/05/judy-miller-curveball-and-mobile.html