Ok, let me see if I've got this straight: you are creating your own chart service based upon the Google Visualization API, and one of your clients is having a problem in IE 9? I'm fairly certain that sublicensing or selling access to the API constitutes a violation of the Terms of Service (see
TOS, section 4, item 1; and section 5, prohibitions on content, item 2). I'm no lawyer though, so I could be wrong there.
Leaving that aside, the IE9 problem appears to be a security issue. The website uses https but accesses your API through http, which throws a security warning in most browsers, but IE 9 blocks the content completely.