Program: 69555
Project: 69555
Buggy source:
/** 
 * @see org.olat.core.gui.components.Form#validate(org.olat.core.gui.UserRequest)
 */
@Override protected boolean validateFormLogic(UserRequest ureq){
  if (!wantCoaches.isSelected(0) && !wantParticipants.isSelected(0) && !wantEmail.isSelected(0)&& !wantOwners.isSelected(0)) {
    recipentsContainer.setErrorKey("String_Node_Str",null);
    return false;
  }
  recipentsContainer.clearError();
  coachesAndPartips.clearError();
  String emailToAdresses=teArElEmailToAdresses.getValue();
  String[] emailAdress=emailToAdresses.split("String_Node_Str");
  teArElEmailToAdresses.clearError();
  if (wantEmail.isSelected(0) && (emailAdress == null || emailAdress.length == 0 || "String_Node_Str".equals(emailAdress[0]))) {
    teArElEmailToAdresses.setErrorKey("String_Node_Str",null);
    return false;
  }
  if ((emailAdress != null) && (emailAdress.length > 0) && (!"String_Node_Str".equals(emailAdress[0]))) {
    this.eList=new ArrayList<String>();
    for (int i=0; i < emailAdress.length; i++) {
      String eAd=emailAdress[i].trim();
      boolean emailok=MailHelper.isValidEmailAddress(eAd);
      if (emailok == false) {
        teArElEmailToAdresses.setErrorKey("String_Node_Str",null);
        return false;
      }
      eList.add(eAd);
    }
  }
  if (wantCoaches.isSelected(0)) {
    if (!coachesChoice.isOneSelected()) {
      coachesChoice.setErrorKey("String_Node_Str",null);
      return false;
    }
    if (coachesChoice.isSelected(2) && (isEmpty(easyAreaCoachSelectionList) || easyAreaCoachSelectionList == null)) {
      if (easyGroupCoachSelectionList.getValue() == null && isEmpty(easyGroupCoachSelectionList) || easyGroupCoachSelectionList.getValue().equals("String_Node_Str")) {
        easyAreaCoachSelectionList.setErrorKey("String_Node_Str",null);
        easyGroupCoachSelectionList.setErrorKey("String_Node_Str",null);
        return false;
      }
    }
  }
  if (wantParticipants.isSelected(0)) {
    if (!participantsChoice.isOneSelected()) {
      participantsChoice.setErrorKey("String_Node_Str",null);
      return false;
    }
    if (participantsChoice.isSelected(2) && (isEmpty(easyAreaParticipantsSelectionList) || easyAreaParticipantsSelectionList == null)) {
      if (easyGroupParticipantsSelectionList.getValue() == null && isEmpty(easyGroupParticipantsSelectionList) || easyGroupParticipantsSelectionList.getValue().equals("String_Node_Str")) {
        easyAreaParticipantsSelectionList.setErrorKey("String_Node_Str",null);
        easyGroupParticipantsSelectionList.setErrorKey("String_Node_Str",null);
        return false;
      }
    }
  }
  return true;
}

Fixed version (ground truth):
/** 
 * @see org.olat.core.gui.components.Form#validate(org.olat.core.gui.UserRequest)
 */
@Override protected boolean validateFormLogic(UserRequest ureq){
  if (!wantCoaches.isSelected(0) && !wantParticipants.isSelected(0) && !wantEmail.isSelected(0)&& !wantOwners.isSelected(0)) {
    recipentsContainer.setErrorKey("String_Node_Str",null);
    return false;
  }
  String emailToAdresses=teArElEmailToAdresses.getValue();
  String[] emailAdress=emailToAdresses.split("String_Node_Str");
  teArElEmailToAdresses.clearError();
  if (wantEmail.isSelected(0) && (emailAdress == null || emailAdress.length == 0 || "String_Node_Str".equals(emailAdress[0]))) {
    teArElEmailToAdresses.setErrorKey("String_Node_Str",null);
    return false;
  }
  if ((emailAdress != null) && (emailAdress.length > 0) && (!"String_Node_Str".equals(emailAdress[0]))) {
    this.eList=new ArrayList<String>();
    for (int i=0; i < emailAdress.length; i++) {
      String eAd=emailAdress[i].trim();
      boolean emailok=MailHelper.isValidEmailAddress(eAd);
      if (emailok == false) {
        teArElEmailToAdresses.setErrorKey("String_Node_Str",null);
        return false;
      }
      eList.add(eAd);
    }
  }
  if (wantCoaches.isSelected(0)) {
    if (!coachesChoice.isOneSelected()) {
      coachesChoice.setErrorKey("String_Node_Str",null);
      return false;
    }
    if (coachesChoice.isSelected(2) && (isEmpty(easyAreaCoachSelectionList) || easyAreaCoachSelectionList == null)) {
      if (easyGroupCoachSelectionList.getValue() == null && isEmpty(easyGroupCoachSelectionList) || easyGroupCoachSelectionList.getValue().equals("String_Node_Str")) {
        easyAreaCoachSelectionList.setErrorKey("String_Node_Str",null);
        easyGroupCoachSelectionList.setErrorKey("String_Node_Str",null);
        return false;
      }
    }
  }
  if (wantParticipants.isSelected(0)) {
    if (!participantsChoice.isOneSelected()) {
      participantsChoice.setErrorKey("String_Node_Str",null);
      return false;
    }
    if (participantsChoice.isSelected(2) && (isEmpty(easyAreaParticipantsSelectionList) || easyAreaParticipantsSelectionList == null)) {
      if (easyGroupParticipantsSelectionList.getValue() == null && isEmpty(easyGroupParticipantsSelectionList) || easyGroupParticipantsSelectionList.getValue().equals("String_Node_Str")) {
        easyAreaParticipantsSelectionList.setErrorKey("String_Node_Str",null);
        easyGroupParticipantsSelectionList.setErrorKey("String_Node_Str",null);
        return false;
      }
    }
  }
  return true;
}