Roy Johnson,
From looking at the source, this error ocurrs if the directory is not defined. Since you know that it is defined, perhaps it isn't where it needs to be?

find({
    no_chdir => 1,
    wanted   => sub {
        print STDERR "*** Doing $_ ***\n";
        if (-f) {
            print "...Adding $_\n"
        }
        elsif (-d _) {
            print "Adding dir $_...\n"
        }
    }},    
    $source_dir   
) or die "$0: $!\n";
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Provided code since wording wasn't clear