How do I set a checkbox to be checked through Lingo in Director 11.5?

I've added a checkbox (the built in flash component) to the stage in my Director 11.5 movie and I can correctly test through script whether the checkbox has been checked or not through the sprite(checkbox).selected property but whenever I display this checkbox again it doesn't remember the last state.

I can set it to be checked or not checked by default in the property inspector but can't find the correct way to update the "selected" property through the script.

I have tried sprite(checkbox).selected = true/1 but this throws a syntax error since .selected is not a valid property of the sprite object.

I assume there must be a way to specify that I wish to update the .selected property of the flash object, but this is my first time using a flash object in my movie and I have been unable to figure this out.

Could somebody please point me in the right direction?

Thanks,
LLMorrisson.