MaskedEditExtender Delete and BackSpace key Issue

1) Create MaskedEditFix.js File

(function(){try{var n=Sys.Extended.UI.MaskedEditBehavior.prototype,t=n._ExecuteNav;n._ExecuteNav=function(n){var i=n.type;i=="keydown"&&(n.type="keypress"),t.apply(this,arguments),n.type=i}}catch(i){return}})()

2) Add to .cs file

 protected void Page_Init(object sender, EventArgs e)
        {
            if (!ClientScript.IsStartupScriptRegistered(GetType(), "MaskedEditFix"))
            {
                ClientScript.RegisterStartupScript(GetType(), "MaskedEditFix", String.Format("", Page.ResolveUrl("../Scripts/MaskedEditFix.js")));
            }
        }