It is important to check always before saving that prefill forms and blank forms are set correctly on the Form Settings tab.

An error can occur when a blank form has been set to prefill contact details, but is also set as the blank form for an RSVP Prefill form.

This error is not a blue shield, or red shield error.  If you are seeing an error message with a blue shield, see this article.

The error can occur because, when a form is set to prefill, it is expecting a UTM parameter that it can use to identify the user.  If a user who, for example, receives the email through the 'forward to a friend method' tries to access the RSVP page, first, it will direct them to the prefill, but as there is no identifying UTM parameter, it will then redirect the user to the blank form, and here lies the issue.

As the user is redirected to the blank form due to the lack of an identifying UTM parameter, if the blank form was set to prefill, it then expects this UTM parameter.  As there isn't one, it then results in an error.

In summary, you must ensure a Blank form is set to 'Blank Form, disconnect from contact' in the Form Settings tab.

If you have confirmed that and are still receiving errors, please reach out to your CSM or raise a support ticket.