On the patient identifier type management screen, turn off the required attribute for the OpenMRS ID identifier type. http://int02.openmrs.org/openmrs/admin/patients/patientIdentifierType.form?patientIdentifierTypeId=3
To have your auto generated identifier display on the form, ensure that the identifier type id that you specified in the setting named “xforms.new_patient_identifier_type_id” is properly configured for auto generation on the screen that looks like this: http://int02.openmrs.org/openmrs/module/idgen/manageAutoGenerationOptions.list