Hi Matt,
There are three possible reasons why you are receiving this message:
1. In "Step 1 of 9" of the wizard, you didn't include the correct URL of your website. If you are submitting the page from anywhere else, other than the URL you've specified, you will get this message. For example if you entered www.myCompanyWebSite.com, but you've submitted the page from your local computer or from www.WrongWebSite.com, you will receive this message. In order to fix it, just move the Web Form to the URL you've specified.
2. If we cannot identify from which URL this page was submitted. I can see this happening, only if you submitted the page from you local computer.
3. If you have not included the "oid" and "formName" parameters that were generated in the last step of the wizard onto the HTML page generated. These are parameters you should see in your Web Forms page (with different values of course):
<input type="hidden" name="oid" value="7Tk5XFDDqO*sJW/5LfI="/>
<input type="hidden" name="formName" value="Web-To-Lead"/>
Thank you
Victor