Index: /tags/ipp-test-20130703/psModules/src/imcombine/pmSubtractionSimple.c
===================================================================
--- /tags/ipp-test-20130703/psModules/src/imcombine/pmSubtractionSimple.c	(revision 35775)
+++ /tags/ipp-test-20130703/psModules/src/imcombine/pmSubtractionSimple.c	(revision 35776)
@@ -353,12 +353,21 @@
     conv1->analysis = psMetadataCopy(conv1->analysis, outAnalysis);
     conv1->data_exists = true;
-    conv1->parent->data_exists = true;
-    conv1->parent->parent->data_exists = true;
+    if (conv1->parent) {
+      conv1->parent->data_exists = true;
+      
+      if (conv1->parent->parent) {
+	conv1->parent->parent->data_exists = true;
+      }
+    }
   }
   if (conv2) {
     conv2->analysis = psMetadataCopy(conv2->analysis, outAnalysis);
     conv2->data_exists = true;
-    conv2->parent->data_exists = true;
-    conv2->parent->parent->data_exists = true;
+    if (conv2->parent) {
+      conv2->parent->data_exists = true;
+      if (conv2->parent->parent) {
+	conv2->parent->parent->data_exists = true;
+      }
+    }
   }