You may find that you need to specify a server for the UserGetAttributes() function. Try obtaining the PDC first and then do the operations.

sub get_PDC {
   #Usage: $pdc=get_PDC($domain);
   my $dom=shift or return undef;
   my $server;
   Win32::NetAdmin::GetDomainController("", $dom, $server);
   return $server;
}
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Then replace "" with $pdc in your userGetAttributes($pdc,...) call.