EJS include is not a function Error

On many of my EJS pages I have the following code:

<%- include('elements/fbviewpagepixel.ejs') %>

It works perfectly fine except on this one page. On that one pages it gives me an error saying include is not a function. It looks like I was able to fix it by changing the code above to the following:

<%- include elements/fbviewpagepixel.ejs %>

Why does the first version work on all of my pages except this one? Why does it give me an error on this one page? What is even the difference between the two?

via Charlie Fish