I received the same error as you guys upgrading from 2.5 to 2.5.1.
Warning: array_keys() [function.array-keys]: The first argument should be an array…
I narrowed it down to this line from the newer wp-config.php:
define('DB_CHARSET', 'utf8');
I use dreamhost, maybe they’re not using utf8? In any case, after removing that line, all was well. I hope this helps someone.
