This time I done following things
while(editorEdit==null || editorEdit.innerHTML.length==0)
editorEdit = document.getElementById('<%= Editor_Edit.ClientID%>');
// alert('hi');
editorEdit.setHTML("hi");
I was thinking that it is taking time to load editor control so I put this in while loop, then I called setHTML method.
I kept whole javascript code at the end of the page.
but still problem persist :( . If i remove comment of alert it works fine.