Error #1009:Cannot access a property or method of a null object reference. [renamed]

Hi, i made a class that creates some sprites and make all those spectrum analyzer effects
when i use this class as the document class of an swf file, it works fine, but if i try to create an instance of this class inside another one, o got this message

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at com.chan.graphics::OvalSpectrumAnalyzer$iinit()
at com.chan.graphics::Teste/com.chan.graphics::frame1()

i don´t understand the explannation on the reference related to this error…

what am i doing wrong, and how can i create an instance of this class?

one thing that i didn’t understand is what means the null object reference

can anyone tell me what´s wrong with my class?

thanks