SSL, File Upload, 404

Hi Guys,

I got a problem, trying to solve it several days but don't really get on
with it. I hope some of you can give me some advise.

I am working with linux and php 4.3.1
I want to upload a file on the server with SSL, accessing the form by
https://www.domain.de/form.html

form.html:
....
<form method="post" enctype="multipart/form-data" action="upload.php">
<input class=standard type=file name=thefile>
....

Now the Problem : Sometimes it works perfectly and the file is being
uploaded by processing the data of the form by upload.php, sometimes the
server generates a 404error after submitting the form.
The Problem does not occur when using http:// !
Can someone tell me why ? Thanx for any help !!

best regards
Matthias Meinecke