Windows.parent doesn't work properly?

I have an overlay using jquery UI which lets the user to log in, when the submit button is hit and the login is successful, the overlay still remains - why might this be? The following code should work but doe开发者_如何学Csn't...

window.parent.location.href = "index";

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try not using parent but top, i have done the same thing in one of my projects and got this error i just used top.

E.G

top.location.href = "index";