Index: gerber.c
===================================================================
--- gerber.c	(revision 29222)
+++ gerber.c	(revision 29223)
@@ -675,7 +675,7 @@
 
 	if (pcb_cam_end(&gerber_cam) == 0)
 		if (!gerber_cam.okempty)
-			pcb_message(PCB_MSG_ERROR, "gerber cam export for '%s' failed to produce any content\n", options[HA_cam].str);
+			pcb_message(PCB_MSG_ERROR, "gerber 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);