Is it possible to Ajax in content from partials?

I'm using a plugin to Ajax in some form content in a modal window. This works as expected in my local PHP dev environment, but it's failing once I move the content into Statamic templates.

Here's the template helper I'm using:

<a href="{{ theme:partial src="/_signup.html" }}"></a>

And here's a screenshot of the error I'm getting:

ajax.png

Is there anything different that I need to do in order to get the info to Ajax in?

(I'm not getting any errors in the console)