Perhaps you should try downloading the library provided by the vendor (the link is on the product page you linked to in your first post, marked "Download Link for Code"). I'd suspect that would have a better chance of working.
And no, I'm not just being a PITA with this--I had a very similar response the first time I tried to use my I2C LCD module (though mine is a 16x2, not a 20x4). If the vendor provides a library, why not try that one first?