Ceditor Not working "s.document.getWindow().$ is undefined"

I am making use of destroy,delete or remove ckeditor instance inside the jquery dialog ui ckeditor loads first works but second time onwards an error is displayed "s.document.getWindow().$ is undefined" or "Cannot read property frameElement of undefined".

    //create the dialog to display the Detailed Email Content
    $("#dvNewEmail").dialog({
        modal: true,
        title: "New Mail",
        width: 900,
        show: "blind",
        position: 'top',
        zindex:-1,
        open: function (event, ui) {
            // delete instance if already exists
            delete CKEDITOR.instances['dvNewMailCkeditor'];
            

            // append the ckeditor
            ckEditorNewMail = CKEDITOR.appendTo('dvNewMailCkeditor', { customConfig: 'GPSConfig.js' }, 'Enter Mail Content');
        },
        close: function (event, ui) {

            // Destroy the ckeditor instance
            ckEditorNewMail.destroy(true);
            ckEditorNewMail = null;
        },
        closeOnEscape: false
     });

    // show the dialog
    $("#dvNewEmail").dialog();