Cant close modal using ajax

[Andres Ignacio Da Viá]

Hi everybody.. im using a modal form which is being called using ajax... 
the problem is im not able to close the form.. i can submit it but not 
close it even from the header or the cancel button.. so i guess the 
data-toggle="modal" attribute is not working as i cannot use 
data-dismiss="modal"

i put some code of what im doing

<!-- Le styles -->

    <link href="assets/css/bootstrap.css" rel="stylesheet">
    <link href="assets/css/smoothness/jquery-ui-1.7.3.custom.css" 
rel="stylesheet">
    
    
<script language="javascript" type="text/javascript" 
src="assets/js/jquery-1.7.2.min.js"></script>
<script language="javascript" type="text/javascript" 
src="assets/js/jquery-ui-1.7.3.custom.min.js"></script>
<script language="javascript" type="text/javascript" 
src="assets/js/bootstrap.js"></script>
<script language="javascript" type="text/javascript" 
src="assets/js/funciones.js"></script>


<li><a href="admins/add_users.php" onclick="cargar(this); return false" 
data-toggle="modal" >Nuevo Usuario</a></li>

////////ajax function/////////

function cargar(obj){
    //$('#spannine').show('slow');
    var uri = obj.href;
    $.ajax({
        url:uri,
        type:'POST',
        success:function(resp){
            $('#spannine').html(resp);
            cargarDatepickers();               
               
        }
    });
}

//////////modal form ////////

<div class="modal" id="modalAdmins"  tabindex="-1" role="dialog" 
aria-labelledby="modalLabel" aria-hidden="true">
  
<form class="form-horizontal" id="form" action="admins/add_users.php" 
method="post" onsubmit="enviarForm(); return false">

<div class="modal-header">
    <button type="button" class="close" data-dismiss="modal">x</button>
    <h3 id="modalLabel">Agregar Nuevo Usuario</h3>
</div>

 <div class="modal-body"> 
 
 <div id="mensaje"></div>
    
    <div class="control-group">
        <label class="control-label" for="inputName">Nombre</label>
        <div class="controls">
        <input type="text" name="name" id="name" maxlength="50" 
onchange="aMayusculas(this);">
        </div>
        </div>
             
    <div class="control-group">  
        <label class="control-label" for="inputEmail">Email</label>
        <div class="controls">
        <input type="text" name="email" id="email" maxlength="80" 
onchange="aMayusculas(this);">
        </div>
        </div>
        </div>

<div class="modal-footer">    
    <input type="hidden" name="grabar" value="si">
    <button class="btn" type="button" data-dismiss="modal">Cancelar</button>
    <input class="btn" type="submit" value="Enviar" onclick="validar();">
    </div>    
</form>

</div>