Index: trunk/BNC/src/orbComp/sp3Comp.cpp
===================================================================
--- trunk/BNC/src/orbComp/sp3Comp.cpp	(revision 6545)
+++ trunk/BNC/src/orbComp/sp3Comp.cpp	(revision 6546)
@@ -306,6 +306,12 @@
       }
       else {
-        epoch->_dr.erase(prn);
-        epoch->_dc.erase(prn);
+        if (epoch) {
+          if (epoch->_dr.find(prn) != epoch->_dr.end()) {
+            epoch->_dr.erase(prn);
+          }
+          if (epoch->_dc.find(prn) != epoch->_dc.end()) {
+            epoch->_dc.erase(prn);
+          }
+        }
       }
     }