This error message could show up when your form or portal has login conditions (rules) that the user is not passing anymore. A change has been made in the time between after the login and before saving the form. Here are some possible scenarios:
1. The user permission has been affected (most common)
For example, while the page was loaded (and before submitting), the user record in Airtable got updated (their access got revoked) and now they're not authorized to save the form anymore.
💡Tip
This reason could also apply when the login condition is based on a linked records field that allows creating records. When a linked record is created, it gets immediately linked to the user record in Airtable (as soon as the child form is closed). Even before the parent form is saved.
The workaround is to use another field on the form to set the user's eligibility condition. A confirmation checkbox field for example.
2. The user record was deleted.
The record was in fact deleted from Airtable.