Problem on Using HTTPService via HTTPS with IE7

I have just developed a simple Flex application by Flex Builder 3. I use the ModuleLoader to load a "Userlogin.swf" module when the Main Application swf start to run . Inside the Userlogin.swf module, I have a HTTPService to connect to my backend PHP server ( I use simple XML format to get the result from the server). The Application run smoothly under IE7 when testing under http protocol. But when I put it into production https protocol, it cannot work ! I orginate the main swf via https protocol. I alway get teh HTTP request error when the Userlogin.swf module access the backend php file. However when it works smoothly on both Firefox and the standalone flash player. Both are via https. Is anyone encouner this problem before and how can I solve it.
One more, if I complier the Userlogin.swf as an application It work smoothly with the https on IE7 !

Regards,