CompuServe Messages

I have been trying to use an existing alpha channel as a mask in Animator Studio without success so far. The only method I have found is "utilities/assemble mask/mask alpha channel". Using this method, the areas that should be opaque (white areas in the alpha channel) come in somewhere around 60% opaque and the areas that should be transparent (black areas in the alpha channel) vary according to the brightness of the image and probably average around 20% opaque. I hope that I am using the wrong function or that I just need to change a setting somewhere. I was really counting on Animator Studio to give me this capability. Any help is appreciated. Thanks Don Hayward