I don't Know What's Happened

Today, my pagerank down from 3 to 0. I don't know what's happened ? Because I have many baclinks with high pagerank, I collect many dofollow baclinks with pr1 up to 5, and I start to update my posting daily. But, my pagerank down.
After I checked in Google Webmasters Tools, I predict that the problem is in an page losing. In my errors report, I saw my "alien" page was losing. The file name is :

http://dailygoodtips.blogspot.com/ps/rpc_relay.html

I don't know what's happened I am really never submit this page in my life. But, why ? Why an illegal content is beeing showed in my blog. This case is seriously will decrease my pagerank because Google hate the error links. But, I am never submit this page.