Index: excellon.c
===================================================================
--- excellon.c	(revision 29222)
+++ excellon.c	(revision 29223)
@@ -288,7 +288,7 @@
 
 	if (pcb_cam_end(&excellon_cam) == 0)
 		if (!excellon_cam.okempty)
-			pcb_message(PCB_MSG_ERROR, "excellon cam export for '%s' failed to produce any content\n", options[HA_cam].str);
+			pcb_message(PCB_MSG_ERROR, "excellon cam export for '%s' failed to produce any content (layer group missing)\n", options[HA_cam].str);
 
 	pcb_drill_uninit(&pdrills);
 	pcb_drill_uninit(&udrills);