How can I prevent a page to jump to top position after failed validation?

You can use the the Page property MaintainScrollPositionOnPostBack :

In the code-behind:

Page.MaintainScrollPositionOnPostBack = true;

or in your webform:

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" MaintainScrollPositionOnPostback="true" %>

Try setting the page focus Page.SetFocus(control); I have an insert button which adds an extra row to my gridview, which is one of many items on a page so I can add Page.SetFocus(control) as the last method in my btnInsert_Click event.

I've found that setting the property:

maintainScrollPositionOnPostBack="true"

in your Web.config <pages> section works well.

I've asked the question on asp.net (http://forums.asp.net/p/1545969/3779312.aspx) and got replies with two solutions. The better one is this piece of Javascript which maintains the scroll position:

<script type="text/javascript">
    window.scrollTo = function( x,y ) 
    {
        return true;
    }
</script>

This is only to put on the page and nowhere to call.

The other solution is similar to RioTera's proposal here (using MaintainScrollPositionOnPostBack) but adds EnableClientScript="false" to the Validators to force a postback. It works too, but the price is an artificial postback.