You could check your document setup (bit size)
and if it is set at 32 or 64 bit, make it 8 bit and this will unlock the doc.
None of the proposed ways works for me.
The little lock icons do not repond and the word Lock: is grayed.
Could it be because it is a .pdf document?
Doesn't work after I Save As .jpg either.
Nor if I first save it as .psd.
if it's the backgrond layer that is always locked. double click on the layer and rename it that should unlock it
Yes, thanks, that unlocks it.
But then comes the next problem:
On top of that layer I have an adjustment layer (Curves), looks fine, but when I merge it down or flatten the image
the effect of the adjustment layer disappears.
I've been merging adjustment layers down like this for many years, all ok.
So why not now?
Man, Why don't you just duplicate it and then delete the lock you don't want? And leave the mystery behind.
Hope it solves your problem
I had the same issue & this solved it.
Top Menu >> Image >> Mode >> Change to sRGB