no assolutamente no submit non e assegnato a nessun elemento mentre form_new_files è assegnato solo al form.

Ma poi scusa se fosse così anche con gli altri browser non dovrebbe funzionare ed invece solo con IE non funziona.

ti passo hrml della pagina:
codice:
<form name="form_new_files" method="post" action="/network/admin/page/upload/save_file.php" enctype="multipart/form-data">
<div style="margin-bottom:20px;">
<div style="float:left; width:200px;"><label for="file_type" class="txt13000">Seleziona il tipo di file</label></div>
<div style="float:left;"><select class="upload" name="file_type" id="file_type" onchange="typefile();">
<option value="">Tipo di file</option>
<option value="audio">Audio</option>
<option value="pdf">PDF</option>
<option value="video">Video</option>
</select></div>
<div id="clear"></div>
</div>

<div style="margin-bottom:20px;">
<input name="file_upload" type="file" style="width:0px; height:0px; visibility:hidden;" onchange="$('div#namefile').text(this.value);" />

<div id="namefile" class="txt13000" style="margin-top:20px;"></div>
<div id="clear"></div>
</div>

<div id="categoria">
<div style="float:left; width:200px;"><label for="category" class="txt13000">Seleziona la categoria</label></div>
<div style="float:left;"><select class="upload" name="categoria" id="category">
<?php $QueryCat=mysql_query("SELECT Filtri FROM categorie WHERE Pagina='Contenuti'") or die (mysql_error());
$filtri=explode("|",mysql_result($QueryCat,0,0));
mysql_free_result($QueryCat);
foreach($filtri as $category){
	echo "<option value=\"$category\">$category</option>";
} ?>
</select></div>
<div id="clear"></div>
</div>

<div style="margin-bottom:20px;">
<div style="float:left; width:200px;"><label for="condizioni" class="txt13000">Condizioni del file:</label></div>
<div style="float:left; width:200px;"><select class="upload" id="condizioni" name="condizioni" onchange="condition(this.value)">
<option value="0">Gratis</option>
<option value="1">A pagamento</option>
</select></div>
<div id="condizioni_prezzo">
<div style="float:left; margin-right:10px;"><label for="prezzo" class="txt13000">&euro;:</label></div>
<div style="float:left;"><input id="prezzo" name="prezzo" type="text" style="width:100px;" class="upload" value="0.00" /></div>
</div>
<div id="clear"></div>
</div>

<div style="margin-bottom:20px;">
<div style="float:left; width:200px;"><label for="nome" class="txt13000">Nome del file:</label></div>
<div style="float:left;"><input id="nome" name="nome" class="upload" type="text" style="width:400px" /></div>
<div id="clear"></div>
</div>

<div style="margin-bottom:20px;">
<div style="float:left; width:200px;"><label for="autore" class="txt13000">Autore:</label></div>
<div><input id="autore" name="autore" class="upload" type="text" style="width:400px" /></div>
</div>

<div style="margin-bottom:20px;">
<div style="float:left; width:200px;"><label for="commento" class="txt13000">Commento:</label></div>
<div><textarea id="commento" name="commento" class="upload"></textarea></div>
</div>

<button type="button" class="bt_save_files" onclick="save_file()">Salva il file</button>
</form>