The fact that one is dealing in a medical office makes the error paramount. The standard applied in instances such as this is the so-called "reasonable person" standard. What does a reasonable person do? Does one ignore the error? Discipline the employee? Notify other parties? It boils down primarily to common sense. The one thing that should NOT be done is to ignore the situation. To do so would constitute actionable negligence. If the employee demonstrates a propensity to make mistakes, then it is a reasonable assumption that it will occur again. Ones responsibility then is to take the necessary steps to prevent the re-occurence of this type situation by whatever means is necessary. Lawyers being lawyers, they will go for the "deep pocket" if injury occurs. Do not allow the situation to continue.