error 'window.opener.document.getelementbyid ... ' is null or not an object

hi all,
i written simple javascript code in prent aspx to open popup window as follows
<script language="javascript">

function openitemserch()
{
    var openitemserch;
    openitemserch = window.open("../../MasterData/ItemSearch.aspx", "openitemserch", "status=1,menubar=0,scrollbars = 1,width=700,height=450,resizable = 0");
window.moveBy(0,0);
}
</script>

from popup winow i want to pass value to its opner by click on grid view row, there is a textbox in opener called txtCode.
In opener window Im inherit master page and also ajax used.text box inside the form view
code written in C# code behind as follows,
 protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName == "SingleClick")
        { ...