Apple issued a Java Update last week via Software Update, and it had a bug in it that could prevent some Java applications from working. Good news though, Apple has fixed the bug, and has released a new update. However, you will want to check to make sure you don’t have the old version still installed.
Try Software Update first, then use the following terminal command to check which version you have installed:/usr/libexec/java_home -v 1.6 -exec java -version
If terminal reports back that you have xM4509, then you’re all set, but if you see xM4508, then Software Update hasn’t fixed it yet, and you’ll need to manually download and install the corrected version from the Apple support site.
You can find more details here.