MemCache::MemCacheError: No connection to server

hi, all
after i switched from nginx + thin to nginx + passenger, the error
“MemCache::MemCacheError: No connection to server” always shows up in
the log. i did what the post
Phusion Passenger and memcache-client revisited –
said in my enviroment.rb, but i still get the same error.

any ideas? thanks a lot