This doesn't happen when I just browse through the site. For example, when I leave the echo line in and just navigate from page to page, the echo appears at the top of the page and it's correct:
C:\xampp\htdocs\__shrinkOffice/libs/
It's only when I try to submit a form that I get the error message. It's happening consistently when I submit a form, though - it's not just one form.