Index: trunk/ppStack/src/ppStackCombinePrepare.c
===================================================================
--- trunk/ppStack/src/ppStackCombinePrepare.c	(revision 26076)
+++ trunk/ppStack/src/ppStackCombinePrepare.c	(revision 27004)
@@ -20,5 +20,5 @@
     ppStackThread *thread = stack->threads->data[0]; // Representative thread
     if (!pmReadoutStackSetOutputSize(&col0, &row0, &numCols, &numRows, thread->readouts)) {
-        psError(PS_ERR_UNKNOWN, false, "problem setting output readout size.");
+        psError(PPSTACK_ERR_ARGUMENTS, false, "problem setting output readout size.");
         return false;
     }
@@ -45,5 +45,5 @@
 
     if (!pmReadoutStackDefineOutput(options->outRO, col0, row0, numCols, numRows, true, true, maskBad)) {
-        psError(PS_ERR_UNKNOWN, false, "Unable to prepare output.");
+        psError(PPSTACK_ERR_ARGUMENTS, false, "Unable to prepare output.");
         return false;
     }