I’m working on a file in PS that has 12 layers. Actually I thought I had finished the file last night. (Should have gone to bed earlier.) When I took another look at the file today, I saw that I could have done a cleaner job of masking on the 5th layer from the top. I’m using PS CS 5.1 Extended.

It would be an easy fix – but I’m unable to select the layer mask for that layer. I tried duplicating the layer, and I can’t select the mask in the duplicate layer either. Either way I can select the layer but not the mask. I even rebooted a couple of times. Same thing.

Since I’ve customized a number of settings and brushes, I’d prefer not to reset PS to the factory defaults, and I’m not even sure that would work in this case.

If it makes a difference, the file is a TIFF file, and the layer is an image layer, not an adjustment layer. (The model’s face had too much red, the arms are too dark, and the skin on her chest, below the arms, is too light, etc. I needed to make minor adjustments to brightness, contrast, hue/sat, etc., and I decided to do those things in ACR rather than have multiple adjustment layers of each type.)

Any ideas?

Turn on the channels palette, and drag the mask channel to the make selection from channel icon. Create new layer and add mask (or switch to the layer you want the mask for and add mask). It'll use the selection to form the new mask.

Or select the mask channel and select all. Switch to the channel you want to add the mask to and paste there.

first thing to check is if the layer is locked.

you can make a new layer, then copy the mask to it then
refine the mask from there.

but, when I've had problems, it's something simple like locked layer,
brush on overlay, or something like that.

I've had funky stuff like this more than once, and after trying everything else, I'll notice that it's in quick mask mode. Then it'll happen again a year later and I'll forget and go through the whole thing all over.