Failed upgrade to 2.7, can’t access admin login

I tried to upgrade a client’s version 2.6 WP blog to version 2.7. I followed the install instructions, taking care not to overwrite the wp-config.php file and the wp-content directory. Now when I try to log in, all I get is a page with this at the top:

d() * * @param int|string $key The cache ID to use for retrieval later * @param mixed $data The data to add to the cache store * @param string $flag The group to add the cache to * @param int $expire When the cache data should be expired * @return unknown */ function wp_cache_add($key, $data, $flag = ”, $expire = 0) { global $wp_object_cache; return $wp_object_cache->add($key, $data, $flag, $expire); } /** * Closes the cache. * * This function has ceased to do anything since WordPress 2.5. The * functionality was removed along with the rest of the persistant cache. This * does not mean that plugins can’t implement this function when they need to * make sure that the cache is cleaned up after WordPress no longer needs it. * * @since 2.0.0 * * @return bool Always returns True */ function wp_cache_close() { return true; } /** * Removes the cache conten

I have no idea what’s going on, because I followed the same procedure to update my own blog, and had no problems.

I’m new to all of this, so some clear suggestions would be greatly appreciated.