Apache Vysper - XMPPServer ClassNotFoundException

Question

I have a short question. I want to create a XMPP server with Apache Vysper. But when I try to create a server:

XMPPServer server = new XMPPServer("myserver.com");

I get a ClassNotFoundException on this line, although the class is imported correctly.

Can Somebody help me out?

Thanks :)

Here the Exception:

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/vysper/xmpp/server/XMPPServer
    at de.seba.vyspertest.App.main(App.java:13)
Caused by: java.lang.ClassNotFoundException: org.apache.vysper.xmpp.server.XMPPServer
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 1 more