Datasetrio,
Coloca esse codigo no form Load da pagina que funciona.
Response.Write(
"<script> window.open('default.aspx',null,'left=300, top=100, height=350, width= 650, status=no, resizable= no, scrollbars= no, toolbar= no,location= no, menubar= no'); </script>")
Abraço
Robson Souza