BZ #153: I2P installer fails with ClassNotFoundException: com.izforge.izpack.util.OsConstraint

Status fields:

The I2P client works well with CACAO/OpenJDK, but the installer fails after unpacking
with

java -jar i2pinstall_0.8.2.exe -console
...
[ Unpacking finished ]
[ ERROR: com.izforge.izpack.util.OsConstraint ]
java.lang.ClassNotFoundException: com.izforge.izpack.util.OsConstraint
        at java.lang.ClassLoader.findClass(ClassLoader.java:373)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:334)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:264)
        at java.io.ObjectInputStream.resolveClass(ObjectInputStream.java:621)
        at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1592)
        at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1513)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1749)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:368)
        at java.util.ArrayList.readObject(ArrayList.java:696)
        at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
        at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:616)
        at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:991)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1865)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346)
        at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1963)
        at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1887)
        at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770)
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:368)
        at com.izforge.izpack.installer.Unpacker.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:636)

The installer works fine with Hotspot/OpenJDK. CACAO is built with current Icedtea6
tree.

You could not possibly have known that this is the same problem, but it is.

*** This bug has been marked as a duplicate of bug 149 ***