[TYPO3] Version 4.1: .htaccess files for faster backend don't seem to work

[Pieter]

Hello all,

the backend of Typo3 gives me all kind of problems if I enable the 
.htaccess files (as explained in 
http://typo3.org/development/articles/release-notes-41/page/4/).

- the graphics of the login screen and the page tree disappear as soon 
as I enable the file in typo3/gfx/
- I get an internal server error (when I go to Web -> Page) with the 
file in typo3/sysext/ enabled or all .htaccess files enabled.  The error 
is only present on the right part of the screen, the menu on the left 
and the page tree keeps on working.

When I run phpinfo in the install tool the "Loaded Modules" list 
contains "mod_expires".
The configuration file of Apache contains "AllowOverride All".  I added 
"AllowOverride Indexes" and restarted but that should not be necessary.

The Apache logfile contains:
GET /t3/typo3/sysext/cms/layout/db_layout.php?id=3 HTTP/1.1" 500 607 
"http://my.site.org/t3/typo3/alt_db_navframe.php??currentSubScript=sysext%2Fcms%2Flayout%2Fdb_layout.php" 
"Mozilla/5.0 (Windows; U; Windows NT 5.1; nl; rv:1.8.1.2) Gecko/20070219 
Firefox/2.0.0.2"

Versions:
Apache/1.3.33 (Debian GNU/Linux) mod_ssl/2.8.22 OpenSSL/0.9.7e 
PHP/4.3.10-19 mod_perl/1.29 DAV/1.0.3
PHP Version 4.3.10-19


Who can tell with this info what goes wrong...?

Kind regards,
Pieter