This may be an issue with the security category of the stationery. In order for stationery to show up as an option for TeamRaiser emails, it must either be set to be in the "General" security category or have a matching security category with the event. Under normal circumstances any stationery that does not fit this requirement will simply not show up as an option when choosing a default stationery, but when you are using blueprints there is a loophole. If the security category of the blueprint is different than the security category of the child events, stationery may show up as an option for the default setting in the blueprint even though it is not possible for the child events to use it. If this is the case, you either want to change the security category of the TeamRaiser to match its blueprint, or change the security category of the stationery to be "General"