I am trying to integrate zk and google app engine. My application works fine on the local environment. But when I upload it to the google app engine , it get the following error.

The resource you request is no longer available: /newRequest.zul (z_tpg).
This is normally caused by timeout, or opening too many Web pages.
You have to reload the page and try again.

Also in the log file of the google app engine I see the following error.

org.zkoss.io.Serializables smartWrite:63: Unable to serialize entry: $BINDER$=org.zkoss.bind.AnnotateBinder@2d2da4

W 2012-03-23 11:53:43.907

/newRequest.zul
java.lang.RuntimeException: java.io.NotSerializableException: java.lang.ref.WeakReference
at com.google.apphosting.runtime.jetty.SessionManager.serialize(SessionManager.java:373)

Any help or direction is appreciated.
I have made the changes to the zk.xml file, web.xml file and the appengine-web.xml file as mentioned here (http://books.zkoss.org/wiki/ZK_Installation_Guide/Setting_up_Servers/Google_App_Engine). I am using zk 6.0 on eclipse 3.7 with app engine 1.6.3