{ denotes a hash, [ denotes array, just like in Perl. You are trying to iterate through $object->{Content_ID} by dereferencing it as an ARRAY but it is a hash, with keys CNBP_021687, CNBP_021688 and CNBP_021691. The correct way to iterate would be:

foreach $key (keys %{$object->{Content_ID}} ){
    my $item = $object->{Content_ID}{$key};
    print " do nothing \n";
};
[download]