What browser are you using?
Also, have you actually uploaded the HTML page and GPX track to some webspace, or are just viewing them on you own computer? I think some browsers have limitations on JavaScript reading local files, so it won’t work if it is just stored on your PC.
Try uploading the page and track somewhere if you can. You could also give a link to your webpage, then I will check if its working, or if anything appears to be wrong.