Cannot login to some sites – no error

Some of my site logins are not working. Some of them are. The user and pass is the same for all of my sites.

On the sites that I cannot log in to, the wp-login.php goes into an infinite loop with no error when I enter the user/pass. (There is no error on php page or in /var/log/apache2/error.log) when I try to log in.

It just redirects me right back to:

wp-login.php?redirect_to=http%3A%2F%SITENAME.com%2Fwp-admin%2F&reauth=1

If I deliberately type the wrong user/pass it DOES show an error.

Recently upgraded WP…

I have a WordPress network with several sites (WPMU) and the sites are all displaying/mapping correctly. I used to be able to login to them. Some are running in maintenance mode…

I’m running WP 3.1.3 on Apache 2.2.8

.htaccess:

# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^[_0-9a-zA-Z-]+/(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^[_0-9a-zA-Z-]+/(.*\.php)$ $1 [L]
RewriteRule . index.php [L]
# END WordPress 

php_value upload_max_filesize 50M
php_value post_max_size 50M
php_value max_execution_time 200
php_value max_input_time 200

Thanks!