My suggestion is to turn off that tinymce editor under admin options and it should work. That is an addon and I can not say if its compatible with IE9. You can also try downloading the tinymce application and replacing the tinymce code under the js directory with newer code from them.
It will be a bit before I get time to actually look at an application we do not provide direct support for. All I can do when I get some time is do what I just told you to do try updating there code and see if it works.