diff --git a/PutTowerPosition/cmd.cs b/PutTowerPosition/cmd.cs
index da3db12..61dc2f2 100644
--- a/PutTowerPosition/cmd.cs
+++ b/PutTowerPosition/cmd.cs
@@ -93,8 +93,15 @@ namespace PutTowerPosition
                         {
                             DBText latestTowerName = acTrans.GetObject(tower.name, OpenMode.ForWrite) as DBText;
                             DBPoint latestTowerPoint = acTrans.GetObject(tower.point, OpenMode.ForWrite) as DBPoint;
-                            latestTowerName.Erase();
-                            latestTowerPoint.Erase();
+                            if (latestTowerName != null)
+                            {
+                                latestTowerName.Erase();
+                            }
+                            if (latestTowerPoint != null)
+                            {
+                                latestTowerPoint.Erase();
+                            }
+                            
                         }
                         latestTowerList.Clear();
                         
@@ -308,7 +315,10 @@ namespace PutTowerPosition
                 }
                 string norm_line;
                 norm_line = Regex.Replace(line, @"\s+", ",");
-                norm_line = norm_line.Substring(1);
+                if (norm_line.StartsWith(","))
+                {
+                    norm_line = norm_line.Substring(1);
+                }
                 string[] sep = norm_line.Split(',');
                 string towerName = sep[0];
                 if (has_tower.ContainsKey(towerName))