Message13174

You tried the obvious things I suppose? (Permissions on the JAR, incomplete or corrupt download, reputable source.) Does this give you a plausible contents list:

jar -tf Downloads\jython-installer-2.7.2.jar >tf.txt

Starts:
META-INF/
META-INF/MANIFEST.MF
Demo/
Demo/applet/
Demo/applet/deprecated/
Demo/awt/

Ends:
tests/java/org/python/tests/props/Readonly.java
tests/java/org/python/util/InterpreterTest.java
tests/java/org/python/util/jythonTest.java
tests/java/org/python/util/jythonTestPlain.java

I don't have a Mac, but a fresh download of the installer worked for me on Windows. Did it get anywhere at all? Obviously it got as far as running the installer classes, but did you get the dialogues, licence, place to install, etc.? Was this during the mass unpacking that follows?