The major.minor version '51.0' is too recent

Run into this Java error today:

The major.minor version ‘51.0’ is too recent for this tool to understand

While this message is rather useless, I figured that it had to do something with our recent switch from Java 6 to Java 7 (OpenJDK 6 to OpenJDK 7, that is). Sure enough, I found an old version of the “tools.jar” in one of our web application. Replaced it with the new one from Java 7 and all is back to normal again.

Hope this helps.