I got an error message very similar to that one when trying to install Java Plugin for Mozilla. In fact, I think it was exactly the same. It went away after I:
1. Symlinked the plugin file rather than copied it. I beleive you said you had done this already, so it shouldn't be a problem.
2. symlinked the java executables, like 'java', 'javac' and the rest into a directory that was in my path, like '/usr/bin'. I found that just exporting the original java directory into my path just didn't work. I don't know why, as I quadruple checked it and have successfully added directories to my path in the past.
Anyway, it works now.
Well, it did work, but then I upgraded to Mozilla 1.3, and so I need the Blackdown Java for GCC 3.2, and haven't got round to downloading it yet