According to the Essentials update 2 (November 2010), both the original Divine Challenge and the Hybrid Divine Challenge damage instance appear to have been errata-ed to be a no action event (yes, placing the mark is still a minor action). This distinction becomes significant when you hybrid a Paladin with a Fighter.
However, it seems that the Online Compendium was either a) not updated with the errata or b) stealth errata-ed to go back to an immediate action.
So who is right, in this case? The errata document or the online compendium?