Strange error ComboBox component

programming flash
1

i use fl.control.ComboBox

mycombobox.visible = false;

and it throw me a strange error,

TypeError: Error #1034: Type Coercion failed: cannot convert fl.events::ComponentEvent@1b469d81 to CustomEvents.CosEvent.
at flash.events::EventDispatcher/flash.events:EventDispatcher::dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at fl.core::UIComponent/set visible()

the “CustomEvents.CosEvent” is my custom event that extend Event,
but however, the combobox i have no assign any addEventListener to it, and howcome it dispatch my custom event?

any know what happen?

thank you very much