How to edit alpha when "target channels are hidden"?

The Photoshop documention, if that's what it can be called, seems to say that I can edit the alpha channel just like any other channel.

But, many times when I try, I get the message "Could not [do whatever it was I wanted to do] because the target channels are hidden." But if I unhide the RGB channels, the edits I want to make mess up the RGB channels.

How do I edit JUST the alpha channel when I get this message?

In the "Channels" tab, make sure the Alpha and RGB channels are visible (the eye symbol next to them should be showing, click on them untill they are). Then observe the blue "selected" highlights on the channel names - at this point, you want to click on them and not the "eye" symbol, you want to keep all of those active. To edit the alpha channel by itself, you'll need to de-select RGB and have only "Alpha" (or whatever the channel name) hilighted. In the image window, any transparent parts will be shaded over in a color (Red by default).

Remember when editing the Alpha directly that you only have greyscale to work with: Black is transparent, white is opaque and shades of grey are everything inbetween.

Thank you very much. Your advice worked perfectly. It was the blue "select" thingy I missed.