I run the script below, but failed with error message "File  doesn't exist at v2tag.pl line 2.", so how should I do?

#!/usr/bin/perl
die "File $ARGV[0] doesn't exist" unless -f $ARGV[0];
use MP3::Mplib;
my $mp3 = MP3::Mplib->new($ARGV[0]);
my $v2tag = $mp3->get_v2tag;
print "Error writing tags of $ARGV[0]\n" unless $mp3->set_v2tag($v2tag,&UTF8);


this script is used to fix the problem "Amarok is not displaying my utf-8 id3v2 tags properly!"

This script takes the filename of the mp3 file you wanna correct as an argument.
You are simply not giving it the filename or a wrong filename.

Do you mean that I have to correct all my mps files with this script one by one?

In its current form: Yes.
But it is rather easy to add a routine that crawls your directories or handles lists of files.

are there any existing scripts which do it recursively, for the perl-ignorant among us?