Are you deploying your web application into the same instance of tomcat that Content Center is running on? Is this just a ui customization, or a full blown app? The cssdksoap.jar is only needed if you are running your app on a server besides the teamsite server.
If it is a separate web application then that jar needs to be either included in the war file for your separate app, or added to the common/lib section of the tomcat instance so it will be seen by your web app.