EDIT

ImpulseVision/FormMain.cs

@@ -345,6 +345,12 @@ where UserID = '{IdUser}'";
                 SqlCommand Cmd = new SqlCommand(QueryDelUser, SCon);
                 Cmd.ExecuteNonQuery();
 
+                QueryDelUser = $@"delete
+from UserTraffic
+where UserID = '{IdUser}'";
+                Cmd = new SqlCommand(QueryDelUser, SCon);
+                Cmd.ExecuteNonQuery();
+
                 QueryDelUser = $@"delete
 from Users
 where ID = '{IdUser}'";