Problem with bootstrap modal window

When I open a modal window with bootstrap I see a white box behind this window, how can I remove this?

I'm using the Bootstrap 3.3.6 library

link "     link     link

<div class="modal fade" id="miModal0" tabindex="-1" role="dialog" aria- 
labelledby="myModalLabel" aria-hidden="true">
<div class="modal-dialog" role="document">
   <div class="modal-content">
       <div class="modal-header">
           <button type="button" class="close" data-dismiss="modal" aria-label="Close">
               <span aria-hidden="true">&times;</span>
           </button>
           <h6 class="modal-title" id="myModalLabel">DiagramaRelaciones</h6>
       </div>
       <div class="modal-body">
           <iframe name="fram" src="Ciencias Sociales\DiagramaRelaciones.png" width="100%" height="100%" frameborder="0" ></iframe>
       </div>
   </div>
 </div>
</div>

This is the button that activates it

<button type="button" class="btn btn-primary btn-lg" data-toggle="modal" 
data-target="#miModal0">DiagramaRelaciones</button>