Can’t load wp-admin/admin.php? page=anything.php

Hello
I have a weird issue with my WP (1.3a5)
Everything runs fine and all, except the plugin admin pages (wp-admin/admin.php?page=…) as for example Spam Karma and Spaminator.
The error I get is the following :
Fatal error: Cannot redeclare url_shorten() (previously declared in /home/altajeux/user/sarl/htdocs/ozh/wp-admin/admin-functions.php:3) in /home/altajeux/user/sarl/htdocs/ozh/wp-admin/admin-functions.php on line 3
(same error whatever the plugin and the requested page)

DrDave (who was really kind to try to help, thanks again) suggested it might be a problem with my PHP version (using 4.2.2) or maybe it’s some weird config options in php (my phpinfo)

Any clue ? anyone had this before ?