I'd take a guess that Firefox is setting the content-type of the form to 'multipart/form-data' when it sees the upload field whereas IE is not - you should put the enctype attribute of the form element ie.: 

   <form method="post" action="whatever" enctype="multipart/form-data"
+>

[download]

/J\

In reply to Re: IE vs. Firefox : Can't use an undefined value as a HASH reference error by gellyfish
in thread IE vs. Firefox : Can't use an undefined value as a HASH reference error by hmbscully

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