I notice that in the code snippet that Kim posted, everything but the top entry (NPL directory) is commented out. You would need to remove the # symbol at the beginning of a line for that entry to become active.
Here is the entry from my localOverrides.conf file, which is working in WW2.7:
$courseFiles{problibs} = {
Library => "NPL Directory",
"Library/Rochester" => "Rochester",
"Library/Rogawski" => "Rogawski 2e",
"Library/UCalgary" => "University of Calgary",
"Library/CollegeOfIdaho" => "College of Idaho",
CAPA => "CAPA",
};
Note that a couple of these are directories that are not part of the OPL, but have been copied into the OPL directory so that they can be indexed by topic.
Danny