Hi Seyed,
You can do this by executing a simple JavaScript on whenever the "refresh" event occurs.
<script type="text/javascript" language="javascript">
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);
function EndRequestHandler(sender, args) {
var TextAreaDiv= document.getElementById("TextAreaDiv");
TextAreaDiv.scrollTop = TextAreaDiv.scrollHeight;
}
</script>
Replace the TextAreaDiv with the ID of Div containing TextArea or of the element providing scroll facility to TextArea.
You need to put this code snippet inside <head> tag or inside the <body>. As you're using UpdatePanel I must assume that you have placed a Script Manager on your aspx page.
Hope this helps!
Happy Coding :)
Sunny_K