Sorry, all I can suggest then is that you have something wrong in your code. I've used those same lines in my homemade pages and they work just fine as long as the rest of the page is coded correctly and all the paths to the files are correct. Did you do your page using one of these articles as a template?
How to create your own vBulletin-powered page! (uses vB templates) or
[How-To] vBulletin API Basics: Creating Custom Pages & Misc.