Selected Index changed not working while using update panel

Add this in your Code behind

protected void GridView1_Distributor_RowCreated(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
e.Row.Attributes.Add("onmouseover",

"this.originalstyle=this.style.backgroundColor;this.style.backgroundColor='#FF9955';");

e.Row.Attributes.Add("style", "cursor:pointer;");

e.Row.Attributes.Add("onmouseout",

"this.style.backgroundColor=this.originalstyle;");


e.Row.ToolTip = "Click to select row";
e.Row.Attributes["onclick"] = this.Page.ClientScript.GetPostBackClientHyperlink(this.grd_Distributor, "Select$" + e.Row.RowIndex);
}
}