Another option is placing an error container outside of your form group ahead of time. The validator will then use it if necessary.
<div class="form-group">
<label class="control-label" for="new-task-due-date">When is the task due?</label>
<div class="input-group date datepicker">
<input type="text" id="new-task-due-date" class="required form-control date" name="dueDate" />
<span class="input-group-addon">
<span class="glyphicon glyphicon-calendar"></span>
</span>
</div>
<label for="new-task-due-date" class="has-error control-label" style="display: none;"></label>
</div>