You only need the runtime environment (RE) to run java apps. From your errors and from what I've read in the 'A different RedHat install problem' from John Fox thread, I think the problem is that you've got Kaffe installed as well. Kaffe is an open source implementation of java that is (mostly) Java 1.1 compliant i.e. it implements an older version of Java.

If you're on an rpm based system you can check if Kaffe is installed by opening a terminal and typing:

rpm -q kaffe

If it is installed, you can remove it by becoming the root user and typing:

rpm -e kaffe

If you really want to keep Kaffe for some reason, another solution is to put the java bin directory as the first directory to be searched in the PATH environment variable.