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Forum Moderators: not2easy
I read a brilliant idea somewhere, and (of course) have never actually used it... but since PS prefs can get corrupted for no apparent reason sometimes, they recommend trashing the prefs you have now, reconfiguring everything exactly to your liking, backing up a duplicate of that new, perfect, pref file, and saving it somewhere. Then, if you ever need to trash your prefs again, you can immediately replace them with a copy of your 'perfect' back up file.
If I ever need to replace my PS prefs, I'll kick myself for not doing that. ;)
If that's not it... are you working on a different layer that what you think you are? Are you actually seeing the red mask being applied?
The error obviously means nothing 'large enough' was selected or masked.