Error message after upload with IE, not with Netscape

Hi all, I wrote a form for the upload of a file and some explaining text. The form is evaluated by a php-script upload.php (see below) and the data (text and file name) are stored in a MySQL-database on a Unix server. The script also shows a thanks-message. The login is controlled by means of .htaccess-files, the transfer is encrypted using SSL. Everything works fine with Netscape and Mozilla, but users of the IE see an error message (re-translated from German to English): Internet Explorer could not open the following internet site: https://www.some-server.de/kk/upload.php?param=abcd&key=0 The connection to the server had been reset. The URI is the upload-script with the right parameters - my retranslation of the message may be wrong. When the user clicks the send button of the form once again, it often works. I should present the important parts of the script here, but as I have no idea which type of a bug it is, I don't know which part is important. Any idea?