INTERNET_FLAG_SECURE in OpenRequest

Does anyone have any experience using the CHttpConnection::OpenRequest
function and supplying INTERNET_FLAG_SECURE to get a secure connection?

I am writing a DLL that needs to post securely to an ASP page. If I call
OpenRequest w/o secure, the DLL works perfectly (calling SendRequest
afterwards of course). However if I specify the SECURE flag it freezes
completely and stops responding. I believe the call freezing is
SendRequest - I don't think it returns from this.

I am using EnableStatusCallback, and it does return
INTERNET_STATUS_CONNECTED_TO_SERVER however it does not ever get past that
(ie INTERNET_STATUS_RECEIVING_RESPONSE)...

Any ideas? We have a security certificate on the server (although it is a 14
day temp one)... Any suggestions at all will be useful - this is essential
to my software!!

Thanks,
Jason