Need help removing background!!

[rdoty]

FYI, the images I'm working on have a grey background (artboard) and there is plenty of contrast, sort of the opposite of the first example, so I'm baffled why it's not working and the results are so inconsistent. Also I get an"error while parsing" notice when I load GIMP (another thread) and that may or may not have an effect and the reason for suggesting a reload.

I've used other graphics and CNC programs in the past (AutoCad, CorelDRAW, etc) and I know there's a learning curve but this is giving me bruises!

Thanks for the input - I'll give it a shot today.