I am receiving the following error when I try to send an overdue notice to a partner using the Account Follow-Up module:

IntegrityError: insert or update on table "mail_message" violates foreign key constraint "mail_message_parent_id_fkey" DETAIL: Key (parent_id)=(3972) is not present in table "mail_message".

2013-12-12 21:57:33,507 1226 ERROR mycompany openerp.netsvc: Integrity Error The operation cannot be completed, probably due to the following: - deletion: you may be trying to delete a record while other records still reference it - creation/update: a mandatory field is not correctly set

[object with reference: Message - mail.message] Traceback (most recent call last): File "/usr/lib/pymodules/python2.7/openerp/netsvc.py", line 292, in dispatch_rpc result = ExportService.getService(service_name).dispatch(method, params) File "/usr/lib/pymodules/python2.7/openerp/service/web_services.py", line 626, in dispatch res = fn(db, uid, params) File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 188, in execute_kw return self.execute(db, uid, obj, method, *args, *kw or {}) File "/usr/lib/pymodules/python2.7/openerp/osv/osv.py", line 172, in wrapper netsvc.abort_response(1, _('Integrity Error'), 'warning', msg) File "/usr/lib/pymodules/python2.7/openerp/netsvc.py", line 71, in abort_response raise openerp.osv.osv.except_osv(description, details) except_osv: ('Integrity Error', 'The operation cannot be completed, probably due to the following:\n- deletion: you may be trying to del ete a record while other records still reference it\n- creation/update: a mandatory field is not correctly set\n\n[object with reference : Message - mail.message]')

Any ideas what might cause this? Sometimes it is successful but most of the time it is not.

Thanks in advance for any help.