BtceDepth not working: 'invalid pair'

[fling-]

…
print Dumper my %depth = %{$btce->BtceDepth('btc_usd')};
…

output:

$VAR1 = 'error';
$VAR2 = 'invalid pair';

but works fine when I copy subs from the modules and run it like

…
print Dumper my %depth = BtceDepth('btc_usd');
…

output:

Reference found where even-sized list expected at bot.pl.wtf line 83.
$VAR1 = {
          'asks' => [
                      [
                        '566.283',
                        '0.01'
                      ],
                      [
                        '568.997',
                        '0.1169'
                      ],
…

And the method is missing from =head1 SYNOPSIS