I downloaded you jar file,
and the class file is located at

However, the java was looking for users/sgeducation/lookang/MagneticField2Wire_pkg/MagneticField2WireApplet.class

You have one more level of structure. That is the reason why it was not working.

Please do not use the same filename as your folder name if you want to add one more level file structure.

Please MagneticField2Wire.xml to users/sgeducation/lookang/MagneticField2Wire.xml
, open it with EJS , rebuild it and upload it again.