Flickering of popup window in .net 3.5

Question

HI ALL,

Below is my code which closes popup window on page load also i want to show the user a message box plz login.. well my popup window gets close but it flickers on the screen is there any way to prevent that.

StringBuilder sb = new StringBuilder();
sb.Append("<script>");

sb.Append("window.close();");

sb.Append("</script");

Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "test", sb.ToString(), false);

MessageBox.Show("Please Sign In first...", "Login Message", MessageBoxButtons.OK, MessageBoxIcon.Question);
return;

Any Help,
Appreciated.
Regards
Kailash kute