strange error in mac

java.lang.NullPointerException
at users.sgeducation.lookang.glimbal8wee02_pkg.glimbal8wee02View.reset(glimbal8wee02View.java:1516)
at org.colos.ejs.library.Animation.reset(Unknown Source)
at users.sgeducation.lookang.glimbal8wee02_pkg.glimbal8wee02Simulation.(glimbal8wee02Simulation.java:23)
at users.sgeducation.lookang.glimbal8wee02_pkg.glimbal8wee02.(glimbal8wee02.java:140)
at users.sgeducation.lookang.glimbal8wee02_pkg.glimbal8wee02Applet.init(glimbal8wee02Applet.java:26)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Plugin2Manager.java:1640)
at java.lang.Thread.run(Thread.java:680)

but run perfectly in Windows.