Ran into an issue where I could not unlock files that were copied from a network location to local disk. The files were marked as being locked, but I was unable to unlock them (through Finder), even though I had all proper rights. Additionally, chmod as root (= user with the highest privileges) did not work either.

Solution

The solution to my issue was to manually override the locked flag of those files, from within a Terminal.

sudo chflags -R nouchg my-problem-file-or-dir

Resetting/clearing the ACL of a file or directory

Additionally, I found that it sometimes is easier to completely reset/clear an ACL, and start over, rather than trying to fix the ACL. This can also be done in a Terminal.

sudo chmod -R -N my-problem-file-or-dir

This completely clears the ACL, leaving only the POSIX permissions intact. From here on out, you can start applying a fresh ACL.