OK, I have never experienced this issue, until the most recent update to Photoshop CC.
So I am assuming this is caused by a bug in the update that was released.
View the video, of which I demonstrate, that this is not just a human mistake, but a possibly glitch in the software.
Once again, I am using the most update-to-date version of PS CC.
Ok, take a look at the tab when you click on the bottom layer. You will see it change to the alpha layer. To edit the alpha, you either need to be in quickmask (lowercase Q) or have a mask attached to the layer.
It is possible, that the layer you have is a copy of the alpha channel.
Because the top layer is not in quickmask mode or no mask you should get that error. When you hit the Q key, the text in the tab changed back to RGB which is what it has to be to edit that layer.
Thanks for the reply Silkrooster.
The only issue I have with that, is what I never had a problem with this before, the latest update to PS.
Why would this be happening now, and it did not happen before?
I have several lesson's up on YouTube, where I am doing something similar, and you never see me experience this issue
Until this latest update release.