Index: trunk/BNC/combination/bnccomb.cpp
===================================================================
--- trunk/BNC/combination/bnccomb.cpp	(revision 3450)
+++ trunk/BNC/combination/bnccomb.cpp	(revision 3451)
@@ -380,5 +380,11 @@
   for (int iPar = 1; iPar <= _params.size(); iPar++) {
     cmbParam* pp = _params[iPar-1];
-    _QQ(iPar,iPar) += pp->sig_P * pp->sig_P;
+    if (pp->sig_P != 0.0) {
+      pp->xx = 0.0;
+      for (int jj = 1; jj <= _params.size(); jj++) {
+        _QQ(iPar, jj) = 0.0;
+      }
+      _QQ(iPar,iPar) = pp->sig_P * pp->sig_P;
+    }
     x0(iPar) = pp->xx;
   }