[Mediawiki-l] Upgrade 1.9.3 -> 1.12.0 fails

[Gsandtner Michael]

We successfully run mediawiki for a year with version 1.9.3 
(with an extension function defining these hooks: 
AutoAuthenticate, SpecialPage_initList, UserLogoutComplete).

Now we tried to upgrade to 1.12.0. The upgrade process seemed 
to be OK, since the installer completed with "Installation 
successfull".
However, it does not work; the error log states:
PHP Fatal error:  Class 'DOMDocument' not found in 
/magwien/var/gondor-phpserver/html/m13wiki/includes/Preprocess
or_DOM.php on line 566
 
Best regards
Michael Gsandtner 
Magistrat der Stadt Wien