As much as I've enjoyed this thrashing about, I guess it's time to confess. When I saw your original post, and did about 60 seconds of Googling, I was pretty sure I knew what the problem is. I haven't done a thorough test, but I'm about 98% sure my first hunch was correct.
Now, what's it worth to both of you to find out how to fix this?
OK, I'll take pity on you. In short, Fancybox is calling upon one of the Google maps API's that's "beyond" the basic functionality. The tipoff is that the error message refers to "geocode," which is a separate service. On my old API keys, it's enabled by default, so the Fancybox maps work. But maybe with a newer key, that's apparently not the case. Just be aware that it's billed at a different rate.
Head for your Google maps API console, then see the series of screenshots attached, in order. After the last step, look for an "enable" button somewhere.