facebook doesn't transfer signed_request in IE7

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Facebook-API

Hi everyone, i have developed a generic facebook app for fan pages. This app can be installed on any page and on each page you see custom content relevant only for this page. In order to do this, i need to receive signed_request from facebook and get fan page id from it. But in some cases in IE7 facebook doesn't transfer signed_request at all.
I have tried to add headers like:
Response.AddHeader("p3p", "CP=\"IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT\"");
or like: Response.AddHeader("P3P: CP", "CAO PSA OUR HONK");

But have so far I do not success to fix it.

Can anyone help me understand why doesn't facebook transfer signed_request in IE7?