Hi Volker,
re: "Would it be possible that I used a "wrong" jar?"
I can tell you that if you turn on DEBUG level logging for org.jboss.remoting, you will see the Remoting version that is being loaded, something like
[13:57:08,280] [main] DEBUG (Logger.java:228) - Remoting version: 2.5.4.SP4 (Flounder)
You should also see something like
[13:57:08,489] [main] DEBUG (Logger.java:228) - Client[970481529:3j001-2i24b0-h8yt4qq7-1-h8yt4qrt-3].connect(null)
which indicates that Client.connect() has been called.
I can't tell you much about the other jars.
-Ron