To summarise even further :) The problem I saw was this...

You have a function which returns a reference to a hash like this:

sub make_hash {
  my %hash;

  # Do clever stuff to fill in values in hash

  return \%hash;
}
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which you call to get a reference to a hash which you store in a scalar called $thisDataset like this:

my $thisDataset = make_hash();
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Later on you pass this hash to another function which assumes that its first parameter is a hash reference like this:

sub do_stuff_to_hash {
  foreach (keys %{$_[0]}) {
    # do something with each key
  }
}

do_something_with_hash($thisDataset);
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All this is fine, but later still you suddenly start to treat $thisDataset as if it's a hash by accesing it like this:

$thisDataset{$curr_month};
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This is the error that use strict picked up as it realised that you were accessing both the scalar $thisDataset and the hash %thisDataset. I suspect that want you really wanted to do was something like:

$thisDataset->{$curr_month};
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use strict is your friend. Use use strict.

--
<http://www.dave.org.uk>

European Perl Conference - Sept 22/24 2000, ICA, London
<http://www.yapc.org/Europe/>