The **best** advice: Don't do "stupid web tricks." They will just annoy your visitors.
The get-it-working-advice: Start from the original working text page again and examine what you are changing a little more carefully. Does your new bug have a different image size? Read the documentation on the free script, if any.
It's also important to clear the cache between changes, this can also give you inconsistent results in testing.
Set up the buggy page (har har) where you can access it via FireFox and open the Error Console prior to loading the page. Load up the page and watch the Error Console carefully, and attempt to decipher it's meaning. It's sometimes vague, but will always report a line number if there are errors.