que es lo que me falla

[pbt]

<p>¿Eres socio del club?*
<input onclick="habilita()" id="si" name="socio" type="radio" value="socio" /><label for="si">Si</label>
<input onclick="deshabilita()" id="no" name="socio" type="radio" value="no socio" /><label for="no">No</label></p>
<p>
Número&nbsp;<input id="num" size="10" maxlength="10" type="text" name="num" value="" class="inputbox" disabled /></p>

<script>
function habilita(){
document.form1.num.disabled=false;
}

function deshabilita(){
document.form1.num.disabled=true;
document.form1.num.value = "";
}
</script>