I was trying to update the content of a modal dialog, and this code works for me:
Try and add the asp:AsyncPostBackTrigger to the asp:GridView's OnRowCommand event and handle the link button click in that event
and in the cs create the event like this
protected void grdListUsers_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "update-something")
{
grdListUsers.SelectedIndex = Convert.ToInt32(e.CommandArgument);
}
}