Answering my own question, the error was actualy indicating that the primary message was blank. In error I tried to attach to attachments to a blank message.

my $msg = MIME::Lite->new(
    'From'    => $param{'from'},
    'To'      => $param{'email'},
    'Subject' => 'Your Report - '.$param{'startdate'}.' to '.$param{'e
+nddate'},
    'Type'    => 'mulitpart/mixed',
    'Data' =>
        'Here is the Report requested for dates '.$param{'startdate'}.
+' to '.$param{'enddate'},
);
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Changing the initial instantiation to the above fixed the error!