What is the most recent pushpool version and where to get it?
Since you tagged your question with litecoin, I believe that you are looking to serve a litecoin pool. For my needs https://github.com/ArtForz/pushpool
did the trick. It added scrypt support and allows you to rewrite the target difficulty (just remove "rpc.target.rewrite": true and replace it with "rpc.target.bits": 18 in the config).