Showcase application -> ace:progressBar.
A JS error occurred when after starting the progressBar on the Polling page, I ckicked on the 'Push' left side link to go to ace:progressBar -> Push page. (IE8). I re-tested several times and this JS error does not happen consistently.

Webpage error details
User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; MDDS; .NET4.0C)
Timestamp: Tue, 31 Jan 2012 16:54:10 UTC

Message: Object required
Line: 65
Char: 13
Code: 0
URI: http://localhost:8080/showcase/javax.faces.resource/bridge.js.jsf?v=703175318


At the same time there was a server error in the log:

31-Jan-2012 9:55:54 AM org.icepush.servlet.EnvironmentAdaptingServlet service
INFO: Falling back to Thread Blocking environment
31-Jan-2012 9:56:06 AM org.icefaces.impl.application.WindowScopeManager callAnnotatedMethod
WARNING: Failed to invokeinterface javax.annotation.PreDestroy on class org.icefaces.samples.showcase.example.compat.progress.LongTaskManager
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 org.icefaces.impl.application.WindowScopeManager.callAnnotatedMethod(WindowScopeManager.java:252)
   at org.icefaces.impl.application.WindowScopeManager.notifyPreDestroy(WindowScopeManager.java:185)
   at org.icefaces.impl.application.WindowScopeManager.notifyPreDestroyForAll(WindowScopeManager.java:177)
   at org.icefaces.impl.application.WindowScopeManager.access$1800(WindowScopeManager.java:42)
   at org.icefaces.impl.application.WindowScopeManager$AllWindowsClosedNotifier.run(WindowScopeManager.java:582)
   at java.util.TimerThread.mainLoop(Timer.java:512)
   at java.util.TimerThread.run(Timer.java:462)
Caused by: java.lang.RuntimeException: FacesContext is not present for thread Thread[WindowScopeManager timer,5,main]
   at org.icefaces.application.PushRenderer.missingFacesContext(PushRenderer.java:226)
   at org.icefaces.application.PushRenderer.removeCurrentSession(PushRenderer.java:121)
   at org.icefaces.samples.showcase.example.compat.progress.LongTaskManager.deinit(LongTaskManager.java:61)
   ... 11 more