It likely requires 32-bit Java, and perhaps changing the settings on the security section of the Java control panel.
If you are using the Oracle Java 7, then it likely won't work at all.
You must be using Apple's Java 6 and set the order of the JRE to 32-bit first.
I don't have Java loaded, so I can't explain the settings well enough. Take a look at the More Like This links on the right side of this page.