[support] Enabling upload module prevents editing nodes

[Aladino Amantini]

Hello to everybody.
I was working with drupal 6.9 and I enabled the upload module, but from 
that moment I was no longer able to edit nodes. I can enter edit mode 
and change the contents but when I click on save or preview button 
drupal returns me the same edit page without the new changes.
The strangest thing is the address that appears in the address bar of 
the browser:

http://www.my_domain/index.php?404;http://www.my_domain:80/node/29/edit

where 29 is the id of the node I want to edit.
It seems a kind of redirect...
This behaviour disappears if I disable the upload module.
I upgraded to the last version of drupal 6 (6.20) and I have done the 
same for the modules, but nothing changed.

This is the list of the modules I have enabled:

-core optional
Database logging	6.20
Help	6.20
Menu	6.20
Path	6.20
PHP filter	6.20
Search	6.20
Taxonomy	6.20
Update status	6.20
Upload	6.20

-core required
Block	6.20
Filter	6.20
Node	6.20
System	6.20
User	6.20

-Meta tags
Nodewords	6.x-1.11
Nodewords - basic meta tags	6.x-1.1
Nodewords - extra meta tags	6.x-1.11
Nodewords - site verification meta tags	6.x-1.1

-Other
Pathauto	6.x-1.5
Token	6.x-1.16
Token actions	6.x-1.16
TokenSTARTER	6.x-1.16

-XML sitemap
XML sitemap	6.x-1.2
XML sitemap engines	6.x-1.2
XML sitemap node	6.x-1.2
XML sitemap taxonomy	6.x-1.2
XML sitemap user	6.x-1.2

Has anybody faced this problem?
May be the problem is not drupal but something else (permissions? web 
server?) but it is strange that occurs only when the upload module is 
enabled.

Thank you for any help.

-- 
Aladino