missing category.inc in category_nodeapi( )

I just had the same issue like http://drupal.org/node/271658
in category_nodeapi( )

Fatal error: Call to undefined function category_node_get_categories() in /var/drupal/6.x/modules-beta/category/category.module on line 796

this helpd me, thus it might be not the solution:
http://drupal.org/node/271658#comment-1288752

might be an issue for hook_init() ?? don't know.