So, it's been years since I waded into something like this. Got out of the IT game and let my geek-brain atrophy. Running 10.5.8 on a Macbook, all system updates look good, etc. I am trying to run a command line program called calibre2opds that extracts the library info from a calibre ebook library and formats for web/Stanza clients. (Check out Calibre if you like ebooks. It's like iTunes for ebooks!) I am apparently running the same Java that the developer is, but am getting a runtime exception. The ONLY difference I can see is he says he's running build 1.6.0_17-b04-248-10M3025 while I am running build 1.6.0_17-b04-248-9M3125. What's the difference there? Code: daxiweida:bin joel$ java -version java version "1.6.0_17" Java(TM) SE Runtime Environment (build 1.6.0_17-b04-248-9M3125) Java HotSpot(TM) 64-Bit Server VM (build 14.3-b01-101, mixed mode) daxiweida:bin joel$ ./calibre2opds ~/Documents/eBooks/ Exception in thread "main" 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 java.net.URLClassLoader.access$100(URLClassLoader.java:56) at java.net.URLClassLoader$1.run(URLClassLoader.java:195) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:317) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:280) at java.lang.ClassLoader.loadClass(ClassLoader.java:252) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:375) daxiweida:bin joel$ I have downloaded and run all 10.5 Java updates from ADC with no results. Just had a baby three weeks ago and I think the lack of sleep is making me miss something very obvious here. Here's the link to the forum where the developer was trying to help me, for reference. http://www.mobileread.com/forums/showthread.php?t=64095&page=5 From my Googlin', it looks like Java 1.6 is troublesome in Leopard perhaps.