RadAsyncUpload throws a javascript error:
SCRIPT16389: System.NullReferenceException: Object reference not set to an instance of an object.
at System.Windows.Browser.ManagedObjectInfo.Invoke(ManagedObject obj, InvokeType invokeType, String memberName, ScriptParam[] args)
at System.Windows.Hosting.ManagedHost.InvokeScriptableMember(IntPtr pHandle, Int32 nMemberID, Int32 nInvokeType, Int32 nArgCount, ScriptParam[] pArgs, ScriptParam& pResult, ExceptionInfo& pExcepInfo)
when Silverlight module is used and uploading is canceled.