Odoo Server Error

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 536, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 573, in dispatch
    result = self._call_function(**self.params)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 309, 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 306, in checked_call
    return self.endpoint(*a, **kw)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 802, in __call__
    return self.method(*args, **kw)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 402, in response_wrap
    response = f(*args, **kw)
  File "/usr/lib/python2.7/dist-packages/openerp/addons/web/controllers/main.py", line 948, in exec_workflow
    return request.session.exec_workflow(model, id, signal)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 1111, in exec_workflow
    r = self.proxy('object').exec_workflow(self.db, self.uid, self.password, model, signal, id)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 878, in proxy_method
    result = dispatch_rpc(self.service_name, method, args)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 114, in dispatch_rpc
    result = dispatch(method, params)
  File "/usr/lib/python2.7/dist-packages/openerp/service/model.py", line 37, in dispatch
    res = fn(db, uid, *params)
  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/service/model.py", line 183, in exec_workflow
    return exec_workflow_cr(cr, uid, obj, signal, *args)
  File "/usr/lib/python2.7/dist-packages/openerp/service/model.py", line 177, in exec_workflow_cr
    return execute_cr(cr, uid, obj, 'signal_workflow', [res_id], signal)[res_id]
  File "/usr/lib/python2.7/dist-packages/openerp/service/model.py", line 159, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  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 3557, in signal_workflow
    result[res_id] = workflow.trg_validate(uid, self._name, res_id, signal, cr)
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/__init__.py", line 85, in trg_validate
    return WorkflowService.new(cr, uid, res_type, res_id).validate(signal)
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/service.py", line 91, in validate
    res2 = wi.validate(signal)
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/instance.py", line 75, in validate
    wi.process(signal=signal, force_running=force_running, stack=stack)
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/workitem.py", line 120, in process
    ok = self._split_test(activity['split_mode'], signal, stack)
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/workitem.py", line 248, in _split_test
    self._join_test(t[0], t[1], stack)
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/workitem.py", line 257, in _join_test
    WorkflowItem.create(self.session, self.record, activity, inst_id, stack=stack)
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/workitem.py", line 95, in create
    workflow_item.process(stack=stack)
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/workitem.py", line 116, in process
    if not self._execute(activity, stack):
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/workitem.py", line 162, in _execute
    returned_action = self.wkf_expr_execute(activity)
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/workitem.py", line 313, in wkf_expr_execute
    return self.wkf_expr_eval_expr(activity['action'])
  File "/usr/lib/python2.7/dist-packages/openerp/workflow/workitem.py", line 291, in wkf_expr_eval_expr
    result = eval(line, env, nocopy=True)
  File "/usr/lib/python2.7/dist-packages/openerp/tools/safe_eval.py", line 314, in safe_eval
    return eval(c, globals_dict, locals_dict)
  File "", line 1, in <module>
  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/addons/account/account_invoice.py", line 923, in action_move_create
    inv.with_context(ctx).write(vals)
  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_thread.py", line 431, in write
    result = super(mail_thread, self).write(cr, uid, ids, values, 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/api.py", line 363, in old_api
    result = method(recs, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/models.py", line 3774, in write
    self._write(old_vals)
  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/models.py", line 4021, in _write
    recs.recompute()
  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 5690, in recompute
    rec._write(values)
  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/models.py", line 3885, in _write
    cr.execute(query, params + (sub_ids,))
  File "/usr/lib/python2.7/dist-packages/openerp/sql_db.py", line 158, in wrapper
    return f(self, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/openerp/sql_db.py", line 234, in execute
    res = self._obj.execute(query, params)
ValueError: "ERREUR:  la valeur d'une cl\xe9 dupliqu\xe9e rompt la contrainte unique \xab account_invoice_number_uniq \xbb
DETAIL:  La cl\xe9 \xab (number, company_id, journal_id, type)=(/, 1, 15, in_invoice) \xbb existe d\xe9j\xe0.
" while evaluating
u'action_move_create()'