click-and-drag, no errors at first, but not working...

[mattwatts15]

I have an array of knobs, they all have functions so that you can click-and-drag left-right or up-down to make them rotate back and forth.
when i have one knob on its own the code works fine. but now that i've put them in an arrary i've confused myself with the code.

theres no errors to start, but when i click on any of the knobs i get this error:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
	at D3264NEW_Scene1_fla::MainTimeline/knobPRESS()

someone said i should put this:currentKnob=e.target;in the knobPRESS function, but then I got an error in the compiler errors when i started it up...

is there a different way to write this, or any other ideas? thanks