As recently was reported by Eurogamer, Bethesda Softworks and Obsidian Entertainment are aware of errors reported by first players of Fallout: New Vegas add-on Honest Hearts.
Currently they are working on a fix that has to resolve most of the issues. There was an information from Nick Breckon that some players may have to start the game over if they wish to play the DLC. However later he has corrected himself.