This line

my @forms = $tree->find_by_tag_name('FORM');
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is probably returning an arrayref, not an array. So when you do this, @forms is actually a 1-element array where the first element is a reference to what you actually want.

If this is the problem, just use a reference and dereference the array appropriately. To wit:

my $forms = $tree->find_by_tag_name('FORM');
die "What, no forms" unless scalar @{$forms};
my $f = HTTP::Request::Form->new($$forms[0], "$IS_URL/$session_id/Serv
+ice/SysAdmin/DataImport/1/2");
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(Forgot to mention: you can see if the function returns an arrayref by looking at ref ($tree->find_by_tag_name('FORM')) -- if it's ARRAY then there's your answer :))

(Addendum: I'm totally wrong about what's going on here. I think you really have a problem with your use of H::R::F::field. Specifically that you can't set DataFile to an arrayref. At least, I don't think you can. That's what I get for not checking the POD...)

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"I hate it when I think myself into a corner."
Matt Mitchell