Jonas install & start

I installed Jonas server on my PC and set my environment according to the
instructions in the documentation. When I run 'jonas check' everything seems
ok, but as soon as I execute 'jonas start' I get this error:

Exception in thread "main" java.lang.NoClassDefFoundError: server
Caused by: java.lang.ClassNotFoundException: server
	at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:276)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
	at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)

Does anyone have any idea what's wrong?

Thanks in advance,

Erik