Problem with servoy-updater.jar

Classic Servoy
1

Hello
I have one server that only has installed servoy_server with the next configuration:

CentOS release 5.4 (Final)
kernel CentOS release 5.4 (Final)

java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Java HotSpot(TM) Server VM (build 16.3-b01, mixed mode)

The problem is when I whant update. From the servoy_server directory I write: java -jar servoy_updater.jar and the result is:

Exception in thread "main" java.lang.NoClassDefFoundError: com/servoy/j2db/util/VersionCheck
Caused by: java.lang.ClassNotFoundException: com.servoy.j2db.util.VersionCheck
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: com.servoy.j2db.util.VersionCheck. Program will exit.

I have read this link http://forum.servoy.com/viewtopic.php?f=1&t=11333#p56683 but:
1.- The servoy_update.jar corresponds to 5.1 version (is not obsolete).
2.- servoy_server/lib/j2db.jar is on the correct path.

Any idea on this?

Thanks.