I have almost the same problem. Below you can find error I've got after selection an Option from Select list with onchange event :

ERROR: 02/06/2009 10:22:07 [com.jniwrapper.util.c] - DomFactory.Proxy.invoke: target = Element <SELECT> id: >ms__id1, method = fireEvent, error = null
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.jniwrapper.win32.ie.dom.j.run(SourceFile:592)
at com.jniwrapper.win32.MessageLoopThread$ThreadSynchronizedAction.run(MessageLoopThread.java:569)
at com.jniwrapper.win32.MessageLoopThread$LoopThread.run(MessageLoopThread.java:511)
Caused by: com.jniwrapper.win32.com.ComException: COM object method returns error code: 0x80070057; E_INVALIDARG (The parameter is incorrect.)
at com.jniwrapper.win32.com.impl.IUnknownImpl.invokeStandardVirtualMethod(SourceFile:725)
at com.jniwrapper.win32.mshtml.impl.IHTMLElement3Impl.fireEvent(IHTMLElement3Impl.java:376)
at com.jniwrapper.win32.ie.dom.c.fireEvent(SourceFile:322)
at com.jniwrapper.win32.ie.dom.c.fireEvent(SourceFile:558)
... 7 more

This isse is very critical!!!