Pyramid ignore custom exception

Question

i think i might have a problem using pyramid and dealing with custom error code / exception

In the back end application, im raising a errareCatalog.errExtapiFulfillIdDeprecated when a specific events occurs, i dont think it's significant but here's what i'm raising in my errareCatalog.py :

class errExtapiFulfillIdDeprecated(errare.processingErrare):
  e_mnemonic = 'ERR_FULFILL_ID_DEPRECATED'
  e_baseMsg = gettext('Fulfill id is deprecated')
  e_errCatalogNumber = -21008

I'm trying to catch this exception in the front end part this way :

from pyramid.httpexceptions import HTTPNotFound
from hll.errors import errareCatalog

try :
  stuff that raise and exception
except errareCatalog.errExtapiFulfillIdDeprecated as ex :
  request.response.status_code = 404
  print 'throwin 404'
  return HTTPNotFound()  

The problem is, i never seem to enter in this except. A 500 error is thrown somewhere and redirect me to the 500 page. Am i doing something wrong with the way i raise / catch exceptions or do i have a configuration missing in Pyramid ?

Edit : here's my exception view

@view_config(context=errareCatalog.errExtapiFulfillIdDeprecated, permission=NO_PERMISSION_REQUIRED)
def mobile_ticket_error(exc, request):
  print 'test error'
  logger.exception("DEPRECATED FULFILLID: %s" % str(exc))   
  return render_to_response("mylogin:templates/mobile-ticket-error.genshi",
                            {'message': str(exc),
                            'layout_name': get_layout_name(request)},
                            request=request)