Many of the forms used by ACU are done through Google Forms. By default, a Google Form created by an ACU account requires that the person filling out the form be logged in to their ACU account. Occasionally, you will see this error if you are also logged in to a personal Google account or a Google account for another organization.
To resolve this issue, log out of any other Google accounts that may be logged in. This can be most easily accomplished by visiting mail.google.com and clicking on your profile in the upper right corner of the page, then selecting "Sign Out".