ShowModalDialog function not returning values

[blindbull]

I have a problem with returning values from a form shown through an IFrame with the ShowModalDialog function.

The code to call the modal dialog is JS and is below:

var vReturnValue;
strModalDialogFrame = 'BuildADIFrame.asp?
parameterList= ' + strPackageList ;

vReturnValue = window.showModalDialog (strModalDialogFrame ,"","strOptions");

alert('a ' + vReturnValue);

The alert box gives a return value of undefined.

Page BuildADIFrame.asp has an IFrame with src of :

SRC="AddaPage.Asp?parameterList=<%=Request.QueryString("parameterList")%>"

The only other thing is the page that is displayed in the modal dialog window.

AddaPage.Asp

The above is displayed correctly. It has to post to itself when a search is carried out, it does this ok. However, when I go to post the results of the select box back the values don't go back. The code I use is :

returnValue=strPageList;
window.close();