Hi,
I try to use SSE in IE9. It doesn’t work because IE9 doesn’t support well the XMLHttpRequest (though the XMLHttpRequest exists, pushed data doesn’t arrive to client). I cannot use custom fields (X-ss-id, etc.) either because XDomainRequest doesn’t allow custom fields (see this link).
IE9 doesn’t support SSE natively which is why the IE SSE shim needs to use XMLHttpRequest as a fallback. In order to support Authentication the SSE Shim needs to support cookies you can test if it does by trying to login with GitHub or Twitter auth at: http://chat.servicestack.net/default_ieshim which is an example of ServiceStack SSE Chat with the IE SSE shim enabled.