drupal forgets clean urls settings

Hi all!
I have the following problem in setting up a drupal site:
followed steps below:
apache 1.3.31 + php 4 + mysql (recent releases).
compiled apache with DSO and inserted rewrite as module; modified php.ini
(as explanied on drupal site) and added database (alwas following the
install file in drupal tarball).
Everything seems to work fine BUT, when I enable Clean URL, it works (with
virtual urls) but althrough saving the configuration, drupal can't remember
it (when I come back to the control panel I find Clean URLs disabled). In
fact It works only for the first link I clic after making it enable, then it
stops working, and I happen it disabled in configuration control panel.
No apache errors.
any idea?
regards,
Marco

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