TypeError: Error #1010: ..WHY?

Hello, I’m just starting with AS3 and am confused by this error:

TypeError: Error #1010: A term is undefined and has no properties.
at com.

It occurs when I don’t remove an event listener that is called for Event.COMPLETE. I am building an app that loads external (local) swf files. When they complete loading, unless i remove the event listener for Event.COMPLETE within the handler function, it calls that error.

Thats fine with me, but I just want to understand what’s going on.

Thanks.