Looks like 11.04 missing javaws.jar. Not sure if it is intentional.
/usr/share/java$ java -version java version "1.6.0_22" OpenJDK Runtime Environment (IcedTea6 1.10.1) (6b22-1.10.1-0ubuntu1) OpenJDK Server VM (build 20.0-b11, mixed mode)
You can try and install Sun (now Oracle) Java version. You can find in that repository ppa:ferramroberto/java. You can add these repositry using that command:
I don't remeber if it is necessery but maybe you have to use