You are right!!! Docu is wrong! But... still no luck at all :( without file:// it shows no error, but still not translating...

#!/usr/bin/perl
use strict;
use Net::MAC::Vendor;

Net::MAC::Vendor::load_cache("/opt/netdb/netmacvendor/oui.txt");

# Vendor code lookup
my $winmac = "90:2b:34:38:44:0d";
my $vendor_ref = Net::MAC::Vendor::fetch_oui_from_cache( $winmac );
print "Vendor is: $vendor_ref \n"
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This outputs nothing...

I am using http://standards.ieee.org/regauth/oui/oui.txt