C#中输入字符串格式异常

未处理的“System.FormatException”类型的异常出现在 System.Windows.Forms.dll 中。其他信息: 输入字符串的格式不正确。
上面是异常信息，下边是报异常的代码：            this.Invoke((EventHandler)(delegate
            {
                //判断是否是显示为16禁止
                if (checkBoxHexView.Checked)
                {
                    //依次的拼接出16进制字符串
                    foreach (byte b in buf)
                    {
                        builder.Append(b.ToString("X2") + " ");
                    }
                }
                else
                {
                    //直接按ASCII规则转换成字符串
                    builder.Append(Encoding.ASCII.GetString(buf));
                }
                //追加的形式添加到文本框末端，并滚动到最后。
                this.txGet.AppendText(builder.ToString());
                string ReceiveText;
                ReceiveText = builder.ToString();
                string[] str = ReceiveText.Split(',');
                foreach (string i in str) ArrText.AppendText(i.ToString()+" ");
                //修改接收计数
                labelGetCount.Text = "Get:" + received_count.ToString();
                ArrText.AppendText("\n");
                CheckSum(str,str.Length);
            }));添加CheckSum（）方法后就报异常，CheckSum（）方法代码：        private void CheckSum(string[] Checkstr,int count)
        {
            count=Checkstr.Length;
            int num;
            int[] CheckSumNum=new int[]{};
            CheckSumNum = Array.ConvertAll<string, int>(Checkstr,s=>int.Parse(s));
            textBox1.Text=CheckSumNum.ToString();
        }