There is a BIG difference between serving wifi to 500 users with just laptops and having 500 users with laptops AND access points in a closed space. It is hard enough to plan for 500 misbehaving client devices, much less if they also had access points. That situation was doomed to fail from the start.
Chris is right. Just deploy a few guys like here for 2.4 http://www.amazon.com/gp/product/B000REU2ZC/ref=oss_product : and here for 5.8: http://www.amazon.com/gp/product/B0002EXJ8Y/ref=oss_product and that will completely wipe out the spectrum before the keynote.