Index: trunk/src/org/openstreetmap/josm/gui/layer/geoimage/ImageViewerDialog.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/layer/geoimage/ImageViewerDialog.java	(revision 18011)
+++ trunk/src/org/openstreetmap/josm/gui/layer/geoimage/ImageViewerDialog.java	(revision 18012)
@@ -609,5 +609,7 @@
     @Override
     public void activeOrEditLayerChanged(ActiveLayerChangeEvent e) {
-        showLayer(e.getSource().getActiveLayer());
+        if (!MainApplication.worker.isShutdown()) {
+            showLayer(e.getSource().getActiveLayer());
+        }
     }