WordPress MU

my config :
server on my localhost (running MAMP)
OS : OS X Leopard

hi all,
I just install WP MU on my localhost, it works except I can't login to the admin panel !
when I type my username and password (the one given when the install is finished) and submit... and I arrived again on the login page, without error message.

what's wrong ?
I already install over 30 regular Wordpress on my localhost and it works fine.

and happy new year !

Running subdomain or subdirectory?

did you install as localhost.localdomain when you installed.

We need slightly more details.

hi,
subdirectory.
I use an address like http://127.0.0.1/wpmu to access to the main blog.
the main blog works, I can open the login page, but can't login to admin page.

define('COOKIE_DOMAIN', FALSE); in the wp-config.php

Thanks jogule, that fixed a similar problem I had. But why? I have 40+ sites in my WPMU install, and only one could not log in. Is there a down-side to setting COOKIE_DOMAIN = FALSE, especially for the 40 sites that didn't need it?