Thanks for Sandeep's help.
They come up with IllegalArgumentException when they try to create ZK components using a working thread along with el expression.
Here is the full stacktrace.
2009/8/4 下午 05:40:36 org.zkoss.zk.ui.metainfo.Property assign:177
嚴重的: Failed to assign [id= ${listbox.uuid}] to
Unknown exception: java.lang.IllegalArgumentException...
