Thread:Project:Support desk/Upgrade from WM 1.15 to 1.20.3 - Cannot Access User Settings - Global default is invalid for field editfont

We upgraded our Intranet MW from 1.15 to 1.20.3 according to http://www.mediawiki.org/wiki/Manual:Upgrading/de

Everything works - Except for accessing User Settings.

Global default '' is invalid for field editfont Backtrace:
 * 1) 0 /var/www/includes/Preferences.php(1243): Preferences::getPreferences(Object(User), Object(RequestContext))
 * 2) 1 /var/www/includes/specials/SpecialPreferences.php(60): Preferences::getFormObject(Object(User), Object(RequestContext))
 * 3) 2 /var/www/includes/SpecialPage.php(611): SpecialPreferences->execute(NULL)
 * 4) 3 /var/www/includes/SpecialPageFactory.php(494): SpecialPage->run(NULL)
 * 5) 4 /var/www/includes/Wiki.php(290): SpecialPageFactory::executePath(Object(Title), Object(RequestContext))
 * 6) 5 /var/www/includes/Wiki.php(536): MediaWiki->performRequest
 * 7) 6 /var/www/includes/Wiki.php(446): MediaWiki->main
 * 8) 7 /var/www/index.php(59): MediaWiki->run
 * 9) 8 {main}

Software	Version MediaWiki	1.20.3 PHP	5.3.3-7+squeeze15 (cgi-fcgi) MySQL	5.1.66-0+squeeze1

Google says there's been a fix in 1.16.2 but we're at 1.20.3 now so this does not help.

Any help would be very appreciated

Best regards, Marcus