HELP: resetDirty method error

NOTE: "ContentBody" is the textarea name

CKEDITOR.instances.ContentBody.on("instanceReady",
function(e)
{
e.editor.setData("AAAA",
function()
{
this.resetDirty();
}
}
)

The code take error on "this.resetDirty()" call, error message is: "object is null or undefined", error code:

getHtml:function(){var i=this.$.innerHTML;"