Some aftermarket ignition modules are especially sensitive to RFI; the most affected are the modules produced by DynaTech. Using resistor type spark plugs such as the NGK CR7HSA will eliminate any RFI troubles. If your scooter doesn't have a computerized module, then either the resistor type or the non-resistor type will work equally well.
Although there is no dimensional or spark output difference between the NGK C7HSA and the NGK CR7HSA plug, the CR7HSA uses an internal resistor. Radio frequency interference (RFI) caused by the spark "jumping the gap" can negatively effect the systems on some modern scooters and motorcycles that have computer controlled ignition or fuel injection systems.