[Mediawiki-l] Upgrade problems

[Jonathan Carter]

Hi List

Please let me know if this isn't entirely the right list to ask questions.

I'm upgrading a mediawiki-1.3.11 installation to mediawiki-1.4.6, and I 
get the error:

Fatal error: Call to a member function on a non-object in 
/var/www/clugwiki2/includes/ObjectCache.php on line 409

when I try to open a page. (Same error when I try to run update.php).

What could be the cause of this, and what can I do to fix it?

Any help would be appreciated.

thank you
Jonathan