You may need to re-evaluate where your error is coming from.. this runs fine on perl 5.8

my %hash = (
        key1 => 1,
        key2 => 2,
        key3 => 3,
        empty => undef,
        string => 'blah',
        string2 => '4',
       );

my @sorted = sort {$hash{$a} <=> $hash{$b}} keys %hash;

print "\nSorted:\n";
foreach(@sorted){ print "$_\n"; }

__END__

prints:

Sorted:
string
empty
key1
key2
key3
string2
[download]

cheers,

J