fix up error serializer
fix up error serializer

indirectlylit/kolibri,mrpau/kolibri,lyw07/kolibri,indirectlylit/kolibri,learningequality/kolibri,learningequality/kolibri,learningequality/kolibri,lyw07/kolibri,learningequality/kolibri,indirectlylit/kolibri,indirectlylit/kolibri,lyw07/kolibri,mrpau/kolibri,mrpau/kolibri,mrpau/kolibri,lyw07/kolibri