Hey Rob,
I just tested the code and everything is working fine for me.
I can see in the link you have at the bottom, that you are pulling the tracking string twice “?c=undefined&s=undefined” and that is why it’s going to the error page.
I’m not sure why it’s doing this and when I test the banner itself I can’t recreate.
Give me a shout and well try to figure it out.
Cheers,
Nick