Odd 3-7-11 error; won't load any longer

This is going to sound bizarre, but I was using 3-7-11 on OSX just fine until it crashed :D. I tried restarting it, and later reinstalling it, and I am consistently getting this message while trying to start the jar from the command line:

Exception in thread "main" java.lang.UnsupportedClassVersionError: weka/clusterers/GraphGramVisualizer : Unsupported major.minor version 51.0

Java version info:

java -version
java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-462-11M4609)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-462, mixed mode)

Any ideas?