[OS X TeX] Error: I can't write on file '(name)'

[Alain Schremmer]

I have a number of files for which I am getting the error message:

    I can't write on file '(name)'

LaTeX Companion 2ed says:

    [the file] is probably read-only or you may not have writing
    permission for its directory.

I suspect the latter for a couple of reasons.

    These files are copies (via ethernet) onto my portable of files on
    my desktop where these work fine.

    I checked the permissions with get info and they are exactly the
    same on both machines.

    There are many such files but not all of them are that way.

Just in case, I made a new copy of the whole mega folder in which all 
the files reside and I reinstalled TeXShop (was 1.40 on the portable) 
and installed GWTeX. No change but I forgot to uninstall the previous 
one. I am still on 10.3.9.

How do I change the "writing permission for its directory"?

Very hopeful regards
--schremmer

P.S. This is a year-old problem which I finally came around trying to 
fix—in preparation for the big move to 10.4

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