I can only think of wrongful disclosure of embargoed material as a reason? 

Wrongful disclosure, really!

When you present at a live conference there is ususally press there to give you exposure for the "special" data that you are presenting. The formate of the confrence has changed. Where will the press be in this new virtual formate? Maybe they desided to halt the stock after the market closes on Thursday and do a press release on their own to get better exposure or something like that. There are a number of reasons that could be the reason for pulling out of the Late Breaker virtual formate. Let it play out a little before you jump to a conclusion that may be way off base.

It seems as though they had something to say at this conference that hasn't already been said so let see what they come up with. The info they have to present may be coming in combination with something else that has just recently materialized, who knows.

tada