In this paper, we describe a plan-based model for the treatment of misunderstandings in NL cooperative dialogue: an utterance is considered coherent if it is related to some of the interactants' intentions by a relation of goal adherence, goal adoption or plan continuation. If none of them is fully satisfied, a misunderstanding is hypothesized and the goal of realigning the interactants' interpretation of the dialogue is adopted by the agent detecting the problem. This goal makes the agent restructure his own contextual interpretation, or induce his partner to do that, according to who made the mistake.