Enabling the debug mode, I got more details:
Error Field Error Value Type DB_Error Code -18 Message DB Error: no such table Mode 16 UserInfo UPDATE civicrm_afform_submission SET contact_id = 123 WHERE contact_id = 456 [nativecode=1146 ** Table 'wordpress.civicrm_afform_submission' doesn't exist] DebugInfo UPDATE civicrm_afform_submission SET contact_id = 123 WHERE contact_id = 456 [nativecode=1146 ** Table 'wordpress.civicrm_afform_submission' doesn't exist]
It looks like this table is created by the Form Builder extension. I tried to enable it but the table is still not created.