\label{numerical_wrong_answers}
The quick explanation is you need to provide an array of incorrect
values to the <numericalresponse> throught the 'incorrect' attribute.
You need to provide at least as many incorrects as 1 less then the
number of bubbles on the exam. You can provide more if you want to.

(in Edit mode there should be an 'Incorrect Answers:' field you can
fill in)

Minimal example problem:

<problem>
  <script type="loncapa/perl">
    $answer=1;
    @incorrects=(2,3,4,5,6,7,8);
  </script>
  <startoutext />
    Correct answer is 1. <br />
  <endouttext />
  <numericalresponse answer="$answer" incorrect="@incorrects">
    <textline />
  </numericalresponse>
</problem>

Let me know if any this fails to work for you.