system.invalidoperationexception

我正在尝试运行这段代码

public Exception SetData(string Data , long NoOfColumnsAllowed)
    {
        try
        {
            con = new SqlCeConnection(conectionstring);
            con.Open();
            transaction = con.BeginTransaction();
            com = new SqlCeCommand();
            com.Transaction = transaction;
            com.CommandText = "Select  count(*) from [Copy]";
            com.Connection = con;
            sdr = com.ExecuteReader();
            while (sdr.Read())
            {
                noOfColumns = sdr.GetInt32(0);
            }

            if (noOfColumns > NoOfColumnsAllowed)
            {
                long NoOfColumsToBeDeleted = noOfColumns - NoOfColumnsAllowed;
                com.CommandText = "delete from [Copy] where Sno<=@sno";
                com.Parameters.AddWithValue("@sno", NoOfColumsToBeDeleted);
                com.ExecuteNonQuery();
            }
            com.CommandText = "Insert into [Copy] (Data) values (@data)";
            com.Parameters.AddWithValue("@data", Data);
            com.ExecuteNonQuery();
            transaction.Commit();
            con.Close();
            return null;
        }
        catch (Exception ex)
        {
            try
            {
                transaction.Rollback();
            }
            catch (Exception)
            {
            }
            con.Close();
            return ex;
        }

    }

Exception occurred -

系统。invalidoperationexception:事务不能如果在此范围内有任何打开的游标，则提交事务。确保所有数据读取器/结果集都是在提交更改前显式关闭

我是新的事务，无法找到任何有价值的解决方案关于打开游标。代码是否有问题，或者我必须明确关闭数据阅读器，如果是，请告诉我如何?