ASP.NET web page goes blank with JavaScript alert()

private void ShowMessage(string Message)
{
  if (!ClientScript.IsClientScriptBlockRegistered("MyMessage"))
  {
    ClientScript.RegisterClientScriptBlock(this.GetType(), "MyMessage", "alert('" + Message + "');", true);
  }
}

public void btnTest_Click(Object sender, EventArgs e)
{
  ShowMessage("Hello World");
}

ScriptManager.RegisterClientScriptBlock(this.Page, typeof(UpdatePanel), "MyMessage", Message, true);

Further Reading

• ClientScriptManager.RegisterClientScriptBlock Method[^]
• ScriptManager.RegisterClientScriptBlock Method[^]