Open window in web ui probleme

Hello,

1-i have created a bsp page test.pdf which has an URL  lv_url

2- in bsp_wd_cmpwb i have a view, which contain page.htm , in Layout i have :

<%
if controller->url is not initial.            " Line 1
  %>                                               " Line 2
<script language="javascript">         " Line 3
window.open("<%= controller->url %>").focus();

</script>
<%
endif   .
%>

The controller->url is filled by 'lv_url in previous events ,  until here its OK .

The problem :

When i click the first time in button(in my view)  its go very well (it shows me test.pdf), but if i click another time in the  button  it shows nothing .

but If i change the url in debugger ( for exemple while pasing by in line 2) and i give http://www.google.com , it works very well .

if i execute after  www.google .com  the 'xxxxxx'  its go very well .

So the problem is i can't execute the same URL two times successively

Thanks for your help