It appears that the newly released Honest Hearts downloadable content for Fallout: New Vegas has some problems with an already known bug that now also prevents players from starting the DLC. Senior Community Manager Nick Breckon writes on the Bethblog that a fix for the bug is on the way. While he initially reported that players already affected by the bug would have to reload an older save or even restart the game, he later corrected himself on the Bethesda forums:
Just talked to the team: the new patch will provide a way to force your companions to leave your party, thus allowing anyone still encountering the ED-E bug to start up Honest Hearts without reverting to a new save or starting a new character. More info on that patch to come.