This error is known to happen when submitting a form if a field type was changed in Airtable while the form was being filled out. A common change that triggers this message is going from a single-select field to a multi-select field.

If your users run into this error, refreshing the page will allow the form to be submitted. However, the already-filled fields will be lost. To avoid losing work, they can copy the content of any field to a text editor and then paste the values into the form again after refreshing the page.

To prevent this error, if your form takes a significant amount of time to be filled out and requires a field type change in Airtable, it's recommended that you perform the field type modification during a low-activity hour for your business.