Index: trunk/psModules/src/imcombine/pmReadoutCombine.c
===================================================================
--- trunk/psModules/src/imcombine/pmReadoutCombine.c	(revision 21363)
+++ trunk/psModules/src/imcombine/pmReadoutCombine.c	(revision 23989)
@@ -384,23 +384,27 @@
             // Combination
             if (!psVectorStats(stats, pixels, errors, mask, 1)) {
-                // Can't do much about it, but it's not worth worrying about
-                psErrorClear();
+		psError(PS_ERR_UNKNOWN, false, "error in pixel stats");
+		return false;
+	    }
+	    
+	    outputImage[yOut][xOut] = psStatsGetValue(stats, params->combine);
+
+	    if (isnan(outputImage[yOut][xOut])) {
                 outputImage[yOut][xOut] = NAN;
                 outputMask[yOut][xOut] = params->blank;
+                sigma->data.F32[yOut][xOut] = NAN;
                 if (params->variances) {
                     outputVariance[yOut][xOut] = NAN;
                 }
-                sigma->data.F32[yOut][xOut] = NAN;
-            } else {
-                outputImage[yOut][xOut] = psStatsGetValue(stats, params->combine);
-                outputMask[yOut][xOut] = isfinite(outputImage[yOut][xOut]) ? 0 : params->blank;
-                if (params->variances) {
-                    float stdev = psStatsGetValue(stats, combineStdev);
-                    outputVariance[yOut][xOut] = PS_SQR(stdev); // Variance
-                    // XXXX this is not the correct formal error.
-                    // also, the weighted mean is not obviously the correct thing here
-                }
-                sigma->data.F32[yOut][xOut] = psStatsGetValue(stats, combineStdev);
-            }
+		continue;
+	    }
+	    outputMask[yOut][xOut] = 0;
+	    sigma->data.F32[yOut][xOut] = psStatsGetValue(stats, combineStdev);
+	    if (params->variances) {
+		float stdev = psStatsGetValue(stats, combineStdev);
+		outputVariance[yOut][xOut] = PS_SQR(stdev); // Variance
+		// XXXX this is not the correct formal error.
+		// also, the weighted mean is not obviously the correct thing here
+	    }
         }
     }