error messages

src/label_map.h

@@ -79,4 +79,13 @@ E: Topology type exceeds system topology type
 The number of bond, angle, etc types exceeds the system setting. See
 the create_box or read_data command for how to specify these values.
 
+E: Type label already exists: type labels must be unique
+
+For a given type-kind (atom types, bond types, etc.), a given type
+label can be assigned to only one numeric type.
+
+E: Type labels cannot start with a number
+
+Self-explanatory.
+
 */