Button aktieviern/deaktiviern

<script language="javascript" type="text/javascript">
  function verifizieren() {
  if (document.check.pruefe[0].checked == true) {
    document.check.schicke.disabled = false;
  } else {
    document.check.schicke.disabled = true;
    }
  }

  </script>
 
  <form action="" method="" name="check">
  <input type="radio" name="pruefe" value="ok" onchange="verifizieren()" />OK<br />
  <input type="radio" name="pruefe" value="nichtok" onchange="verifizieren()" />Nicht OK<br />
  <input type="submit" name="schicke" disabled="disabled" />
  </form>