02-18-2014 11:55 AM
Add the following code on the Page Load
StringBuilder style = new StringBuilder();
style.AppendLine("var myClass = document.getElementsByClassName('dijitDialogCloseIcon');");
style.AppendLine("myClass[0].style.visibility='hidden';");
ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "", style.ToString(), true);
Enjoy!