Storage.xml can not access because it is used another process

this.stream = new FileStream("storage.xml", FileMode.OpenOrCreate);
/*storage.xml used by another process */
           this.service = new AnnotationService(this.flowRdr1);
           this.store = new XmlStreamStore(this.stream);
           this.store.AutoFlush = true;
           this.service.Enable(this.store);
           // Detect when annotations are added or deleted
           this.service.Store.StoreContentChanged += new StoreContentChangedEventHandler(AnnotationStore_StoreContentChanged);
           // Bind to annotations in store
           BindToAnnotations(this.store.GetAnnotations());