Simple test Java app runs fine under Eclipse, and from a WinDoze command line, but fails on the 400.

I have a simple Java 6 test program, just one class:

import java.nio.charset.*;
public class Test18jn2012 {
public static void main(String[] args) {
String str = "I like Spam.";
byte[] bytes;
bytes = str.getBytes(Charset.defaultCharset());
for (int i=0; i < bytes.length; i++) System.out.print(bytes[i] + " "); System.out.println();
}
}

It executes just fine in Eclipse. It executes just fine on a WinDoze command line, even if I move it to a different directory from where I'd compiled it into.

But when I FTP Test18jn2012.class to the IFS root on our 400, and I try
java Test18jn2012
from either a regular command line or a QShell command line, I get:

Exception in thread "main" java.lang.UnsupportedClassVersionError: (Test18jn2012) bad major version at offset=6 at java.lang.ClassLoader.defineClassImpl(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:267) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:151) at java.net.URLClassLoader.defineClass(URLClassLoader.java:600) at java.net.URLClassLoader.access$400(URLClassLoader.java:124) at java.net.URLClassLoader$ClassFinder.run(URLClassLoader.java:1055) at java.security.AccessController.doPrivileged(AccessController.java:274) at java.net.URLClassLoader.findClass(URLClassLoader.java:492) at java.lang.ClassLoader.loadClass(ClassLoader.java:640) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) at java.lang.ClassLoader.loadClass(ClassLoader.java:606) Java program completed with exit code 1

and if I try
JAVA CLASS(Test18jn2012) CLASSPATH('/qibm/ProdData/Java400/jdk6')
I get

Exception in thread "main" java.lang.NoClassDefFoundError: Test18jn2012 Caused by: java.lang.ClassNotFoundException: Test18jn2012 at java.net.URLClassLoader.findClass(URLClassLoader.java:497) at java.lang.ClassLoader.loadClass(ClassLoader.java:640) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
at java.lang.ClassLoader.loadClass(ClassLoader.java:606) Java program completed with exit code 1

I'm obviously doing something wrong, but WHAT?

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JHHL