OS X 10.5.8 Java Issues

java.lang.UnsupportedClassVersionError: Bad version number in .class file
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:676)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:592)
	at sun.plugin2.applet.Plugin2ClassLoader.defineClassHelper(Plugin2ClassLoader.java:1014)
	at sun.plugin2.applet.Plugin2ClassLoader.access$100(Plugin2ClassLoader.java:69)
	at sun.plugin2.applet.Plugin2ClassLoader$2.run(Plugin2ClassLoader.java:991)
	at java.security.AccessController.doPrivileged(Native Method)
	at sun.plugin2.applet.Plugin2ClassLoader.findClassHelper(Plugin2ClassLoader.java:955)
	at sun.plugin2.applet.Applet2ClassLoader.findClass(Applet2ClassLoader.java:134)
	at sun.plugin2.applet.Plugin2ClassLoader.loadClass0(Plugin2ClassLoader.java:250)
	at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Plugin2ClassLoader.java:180)
	at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Plugin2ClassLoader.java:161)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
	at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Plugin2ClassLoader.java:675)
	at sun.plugin2.applet.Plugin2Manager.createApplet(Plugin2Manager.java:3046)
	at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Plugin2Manager.java:1498)
	at java.lang.Thread.run(Thread.java:655)
Exception: java.lang.UnsupportedClassVersionError: Bad version number in .class file