CRM 4.0 - Iframe de solo lectura

function OnIframeTestReady()
{
    //Override the onmousedown event
    crmForm.all.IFRAME_MyIframe.contentWindow.document.onmousedown = function(){
                alert("La ventana es de solo lectura");
                return false;
    };
}

crmForm.all.IFRAME_MyIframe.attachEvent( "onreadystatechange" , OnIframeTestReady );
crmForm.all.IFRAME_MyIframe.src = "../isv/myweb/default.aspx?so=JTX-05012-7SCRY";