Button to open iframe in lightbox keep showing page not found

Hi

I remember through the past support sites, using this code Open Google seem to work.
But i tried it on the button, it opens a lightbox, and shows my wordpress page not found instead.

Can you tell me what else am i missing?

I need a lightbox popup iframe that displays a contact form page. (Got tired looking for an opt in plugin that allows full customization)

Thanks!