It means that the Activity cannot be displayed because it is still trying to complete execution; meanwhile the ActivityManager has timed out.
I had the same problem, and managed to resolve it by tidying up dependencies between Activity objects.
I would recommend starting up the debugger. Look at any 'services' that your Activity depends on (e.g. http client, parsers etc.) and check that it is not blocking. If you have 'services' that are shared between Activity objects, it might also be worth checking that they still exist in memory as GC may have destroyed any statically referenced service objects or objects cached as WeakReference objects.
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