Today when one of the users tried to send a new message this error appeared. It's a first time since I started using Odoo so it's not a disaster but ..... it can be a bit .... annoying.

Odoo Server Error Traceback (most recent call last): File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 530, in _handle_exception return super(JsonRequest, self)._handle_exception(exception) File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 567, in dispatch result = self._call_function(**self.params) File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 303, in _call_function return checked_call(self.db, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/service/model.py", line 113, in wrapper return f(dbname, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 300, in checked_call return self.endpoint(*a, **kw) File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 796, in __call__ return self.method(*args, **kw) File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 396, in response_wrap response = f(*args, **kw) File "/usr/lib/python2.7/dist-packages/openerp/addons/web/controllers/main.py", line 949, in call_kw return self._call_kw(model, method, args, kwargs) File "/usr/lib/python2.7/dist-packages/openerp/addons/web/controllers/main.py", line 941, in _call_kw return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 241, in wrapper return old_api(self, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/addons/mail/mail_message.py", line 564, in message_read parent_tree[tree_parent_id].append(self._message_read_dict(cr, uid, message_tree[message_id], parent_id=tree_parent_id, context=context)) File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 241, in wrapper return old_api(self, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/addons/mail/mail_message.py", line 407, in _message_read_dict 'is_favorite': message.starred, File "/usr/lib/python2.7/dist-packages/openerp/fields.py", line 765, in __get__ self.determine_value(record) File "/usr/lib/python2.7/dist-packages/openerp/fields.py", line 858, in determine_value record._prefetch_field(self) File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 239, in wrapper return new_api(self, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/models.py", line 3212, in _prefetch_field result = records.read(list(fnames), load='_classic_write') File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 239, in wrapper return new_api(self, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 546, in new_api result = method(self._model, cr, uid, self.ids, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/addons/mail/mail_message.py", line 822, in read self.check_access_rule(cr, uid, ids, 'read', context=context) File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 241, in wrapper return old_api(self, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/addons/website_mail/models/mail_message.py", line 89, in check_access_rule return super(MailMessage, self).check_access_rule(cr, uid, ids=ids, operation=operation, context=context) File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 241, in wrapper return old_api(self, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/addons/mail/mail_message.py", line 733, in check_access_rule notified_ids = [notification.message_id.id for notification in not_obj.browse(cr, SUPERUSER_ID, not_ids, context=context)] File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 241, in wrapper return old_api(self, *args, **kwargs) File "/usr/lib/python2.7/dist-packages/openerp/models.py", line 5189, in browse return self._browse(Environment(cr, uid, context or {}), ids) File "/usr/lib/python2.7/dist-packages/openerp/api.py", line 703, in __new__ for env in envs: File "/usr/lib/python2.7/_weakrefset.py", line 60, in __iter__ for itemref in self.data: RuntimeError: Set changed size during iteration

Any ideas what can cause this problem ?