Thank you for you comment. I discovered the cause of the problem and talk with my colleagues.
Infact it happens that, if you attempt to upload through a form the following line (? is this a Ie/Mozilla bug?!?):
//page.headerData.1.value = <sc ript>alert(document.compatMode);</script>
(note: I've put a 'space char' between 'sc' and 'ript' to ensule this upload...
in the middle of a long text, explorer (or the server?) stops the upload immediately before the line and doesn't upoload the remaining text.
If you are using explorer you will redirected toward a page with "Documents contain no data" and under Mozilla you will receive an alert such as "No data.".
The behaviour changes between different servers, so that I think could be depending from the configuration...
This is very strange... thank you, have luck!!!!!