If sounds like you either have a missing or misconfigured browser plug-in. If you are using Safari, you should be able to disable all current plug-ins one at a time untll the error disappears. This should give you an idea on which one is the problematic one.
Sorry, but this is not really an AirPort networking issue but one related to your browser. As such you may get better responses to your issue if you post your question in one of the OS X areas of the Apple Support Communities.