The problem will be that somwhere in your code you have:

$authors{$_}++ for @authors;
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This sets the value held in $authors{'some_author'} = 1 In a hash of hashes this value is not supposed to be 1 - it is required to be a reference to the nested hash. When you do ${$authors{$from}}{$buddy}++ #same as $authors{$from}->{$buddy}++ Perl is trying to dereference the value 1 which fails as you see. Try something like:

# set authors hash to empty hash refs
$authors{$_} = {} for @authors

# you code goes here
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And it will work. BTW in your inner loop you might as well use values rather than keys as you only use the key to get the value anyway.

cheers

tachyon

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