WordPress MU

Hello
I can't enable WP Backend Menus from admin area.
Every time try to enable it , the page return – out of admin area - to main page of blog.
After some days , I can enabled and disabled it , bout now I don't!
What the wrong?
Can I able to enable plugins menu without entering to admin area.?
Thank you

Are you using the Cimy Extra User Fields plugin by any chance? I had some weird problems when I tried it out on mu. I ended up just forcing it through the database by adding the serialized value of array('plugins'=>1) (as a PHP array) to wp_sitemeta under the meta_key of menu_items.

HTH