Why Johnny can't troubleshoot.

[boo_radley]

using psi::esp, I bet you're trying to get an id3 tag on a directory, maybe . or ..
try changing

my ($title, $artist, $mp3_file);

foreach my $file (@file_names) {
    $mp3_file = new MP3::ID3v1Tag("$file");
    $title = $mp3_file->get_title();
    $artist = $mp3_file ->get_artist();

    print "$title - artist\n";
}

to

my ($title, $artist, $mp3_file);

foreach my $file (@file_names) {
    print "now working with file '$file'\n";
    # remove mp3_file from the my declaration outside the loop
    my $mp3_file = new MP3::ID3v1Tag("$file");
    die "Can't create id tag : $!" unless $mp3_file;
    $title = $mp3_file->get_title();
    $artist = $mp3_file ->get_artist();

    print "$title - artist\n";
}

to get a more detailed error message. Also use -d to determine if $file is really a directory and take appropriate action.