You can't use adjustment layers to tweak alpha channel masks. You must use levels directly to the copied channel. You can clean up using a black and white brush with the brush mode set to Overlay.
Thanks Trevor, the problem is that I am getting a cghannel mask rather than a levels adjustment on the channel when I click on Layers>Adjustment Layers> Levels
OK, I wonder if I am getting confused about what you want to do? If you are trying increase the contrast of your new alpha channel, then Adjustment layers won't work. You have to go Image > Adjust > Levels with the alpha channel selected, and the other chanels turned off.
Is that what you are trying to do, or something else?
Thanks that is exactly the step I was confused about. I was trying to use an Adjustment Layer instead of the Image>adjust command.
You have been a great help