Form Error Message: Automated form submissions not accepted.

I'm getting a strange blocking form error when I try to submit a form. It shows the standard marketo error text above the button: "Automated form submissions not accepted." Anyone ever see this error message before?

Is there a place I can look through Marketo's validation code and see what is going on? I'm filling out the form fields in the same way I would any other form and we've used this LP template without issue in the past.

Thanks,

-D