VS 2008 - Popup Window Can't Read A Text Box

I have a popup window (.aspx page). It will called from a parent .aspx page. All I want to do is read the name of the parent aspx page. I can do that also without issue. Based on the name of the parent window, in the page_load event of the popup window, I want to execute some code.

But the only catch is I am not able to read the parent window name until the page_load event complets the execution.

1. calling popup window from parent window.

Code:
function OpenWindow_HistoricalRuns() {
var windowIncsimHistRuns = window.open('MVal.aspx', 'Market', 'width=350,height=425,scrollbars=0');
windowIncsimHistRuns.moveTo(500, 300);
}

In the body of the popup window the following function tries to read the parent window name:

Code:
function SetDisplay() {
document.getElementById('<%=TextBoxSourcePageName.ClientID%>').value = window.parent.name;
}

In the page_load event of the popup window, I want to see what is value of TextBoxSourcePageName control. I hoped I will get 'MarketVal'. But I never get anything.

Code:
protected void Page_Load(object sender, EventArgs e)
{
if (!this.IsPostBack)
{
try
{
if (TextBoxSourcePageName.Text == "MarketVal")
}
}
}