Index: trunk/ppSub/src/ppSubCamera.c
===================================================================
--- trunk/ppSub/src/ppSubCamera.c	(revision 14741)
+++ trunk/ppSub/src/ppSubCamera.c	(revision 14806)
@@ -28,5 +28,5 @@
     pmFPAfile *inputMask = pmFPAfileBindFromArgs(&status, input, config, "PPSUB.INPUT.MASK", "INPUT.MASK");
     if (!status) {
-        psError (PS_ERR_UNKNOWN, false, "failed to load find definition");
+        psError (PS_ERR_UNKNOWN, false, "Failed to load file definition PPSUB.INPUT.MASK");
         return NULL;
     }
@@ -39,5 +39,5 @@
     pmFPAfile *inputWeight = pmFPAfileBindFromArgs(&status, input, config, "PPSUB.INPUT.WEIGHT", "INPUT.WEIGHT");
     if (!status) {
-        psError (PS_ERR_UNKNOWN, false, "failed to load find definition");
+        psError (PS_ERR_UNKNOWN, false, "Failed to load file definition PPSUB.INPUT.WEIGHT");
         return NULL;
     }
@@ -62,5 +62,5 @@
     pmFPAfile *refMask = pmFPAfileBindFromArgs(&status, ref, config, "PPSUB.REF.MASK", "REF.MASK");
     if (!status) {
-        psError (PS_ERR_UNKNOWN, false, "failed to load find definition");
+        psError (PS_ERR_UNKNOWN, false, "Failed to load file definition PPSUB.REF.MASK");
         return NULL;
     }
@@ -73,5 +73,5 @@
     pmFPAfile *refWeight = pmFPAfileBindFromArgs(&status, ref, config, "PPSUB.REF.WEIGHT", "REF.WEIGHT");
     if (!status) {
-        psError (PS_ERR_UNKNOWN, false, "failed to load find definition");
+        psError (PS_ERR_UNKNOWN, false, "Failed to load file definition PPSUB.REF.WEIGHT");
         return NULL;
     }
@@ -128,4 +128,14 @@
     psFree(view);
 
+    pmFPAfile *sources = pmFPAfileBindFromArgs(&status, input, config, "PPSUB.SOURCES", "SOURCES");
+    if (!sources) {
+        psError(PS_ERR_IO, false, "Failed to load file definition PPSUB.SOURCES");
+        return false;
+    }
+    if (ref->type != PM_FPA_FILE_CMF) {
+        psError(PS_ERR_IO, true, "PPSUB.SOURCES is not of type CMF");
+        return false;
+    }
+
     // psPhot input
     if (psMetadataLookup(config->arguments, "PSPHOT.PSF")) {