@Clueless: head on over to your wp-config.php file and comment out or erase the lines that read ‘define(‘…’);’ and save that file. Now log back into your back-end of WPMU and you’ll see that a note is at the top with newly generated values for ALL of these things.
Now take those values and put them back into your wp-config.php file and save. Use those values for the cookies/salts for everything.
Those are the values to use, hope that helps!