Python - ValueError: incomplete format

buenas comunidad, si alguien conoce del programa odoo que es en python y htmil, me da el siguiente error.... agradecería toda la ayuda:
Traceback (most recent call last):
File "/opt/odoo/addons/website/models/ir_http.py", line 242, in _handle_exception
response = super(ir_http, self)._handle_exception(exception)
File "/opt/odoo/openerp/addons/base/ir/ir_http.py", line 157, in _handle_exception
return request._handle_exception(exception)
File "/opt/odoo/openerp/http.py", line 781, in _handle_exception
return super(HttpRequest, self)._handle_exception(exception)
File "/opt/odoo/openerp/addons/base/ir/ir_http.py", line 182, in _dispatch
result = request.dispatch()
File "/opt/odoo/openerp/http.py", line 840, in dispatch
r = self._call_function(**self.params)
File "/opt/odoo/openerp/http.py", line 316, in _call_function
return checked_call(self.db, *args, **kwargs)
File "/opt/odoo/openerp/service/model.py", line 118, in wrapper
return f(dbname, *args, **kwargs)
File "/opt/odoo/openerp/http.py", line 309, in checked_call
result = self.endpoint(*a, **kw)
File "/opt/odoo/openerp/http.py", line 959, in __call__
return self.method(*args, **kw)
File "/opt/odoo/openerp/http.py", line 509, in response_wrap
response = f(*args, **kw)
File "/opt/odoo/addons/website_event_sale/controllers/main.py", line 45, in registration_confirm
cart_values = order.with_context(event_ticket_id=ticket.id)._cart_update(product_id=ticket.product_id.id, add_qty=1, registration_data=[registration])
File "/opt/odoo/openerp/api.py", line 248, in wrapper
return new_api(self, *args, **kwargs)
File "/opt/odoo/openerp/api.py", line 574, in new_api
result = method(self._model, cr, uid, self.ids, *args, **old_kwargs)
File "/opt/odoo/addons/website_event_sale/models/sale_order.py", line 99, in _cart_update
line._update_registrations(confirm=False, registration_data=kwargs.get('registration_data', []))
File "/opt/odoo/openerp/api.py", line 248, in wrapper
return new_api(self, *args, **kwargs)
File "/opt/odoo/addons/event_sale/models/sale_order.py", line 75, in _update_registrations
Registration._prepare_attendee_values(registration))
File "/opt/odoo/openerp/api.py", line 248, in wrapper
return new_api(self, *args, **kwargs)
File "/opt/odoo/addons/event_sale/models/event.py", line 170, in create
'ticket': res.event_ticket_id and _(' with ticket %s') % (('<i>%s</i>') % res.event_ticket_id.name) or '',
ValueError: incomplete format