IF and onEnterFrame problems

Hello there, I’m having this in my flash site, it’s for tweening an object…

_root.changeSlide = function() {
    // get rid of current slide
    _root.listenfor.onEnterFrame = function() {
            _root.logo._x = _root.logo._x - ((_root.logo._x +550)*.5)/10;
            if (root.logo._x < -500) {

The object starts at the center of the stage, and when tracing the _root.logo._x value (the objects X value) Flash gives me values over -500 (the values go up to -549.05). The problem is, that the IF sentence never goes true. Flash never traces “great success!”.

What is the problem here?.. Can anyone help. Thank you very much!