If i write this code it doesn't work (nothing happens when click the button "Aceptar"). This only happens in PHP field, on another page works well. Why?

<form name="selector"><select name="pagina"> <option selected="selected" value="">- Elegir -</option>
<option value="http://URL">Alojamiento</option>
<option value="http://URL">Comercio</option></select>
<input onclick="window.location=document.selector.pagina.options[document.selector.pagina.selectedIndex].value" type="button" name="go" value="Aceptar" /></form>