1) Must use xhtml or chrml
2) Must put the code on absolut top of the page. In case of in the bottom it will be in the middle of a php request and the page wont work at all.
3) When testing, use the option to see the google banner in the adord code generation page. If you can see the banner when testing, it works. Google will only say that it is verified if you first click on your actual advertise before testing the conversion.