Probe y nada
Tengo este mas abajo y me funciona
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<td> <input name="matriz" type="radio" tabindex=40 onClick="activar(mat,false)" value="Si">
Si </td>
<td> <input name="matriz" type="radio" onClick="activar(mat,true)" value="No" checked>
No </td>
</tr>
</table>
<select name="matriz_n_e" disabled="TRUE" id="mat" class="fBlan" tabindex=41 onfocus="this.className='fCafe'" onblur="this.className='fBlan'">
<option>------</option>
<option value="NUEVA" selected>Nueva</option>
<option value="EXISTENTE">Existente</option>
</select>
***////que raro no
