不明白的数组越界?数组的游标总是莫名的比数组大小大一

代码 如下:
for (var i = 0; i < datasInfo.Count; i++)
{
WriteLog("第" + (i + 1) + "组数据" + "开始下载");
Console.WriteLine("第" + (i + 1) + "组数据" + "开始下载");
string path = PATH + datasInfo[i].CreatedBy + "\\";
if (!Directory.Exists(path))
{
Directory.CreateDirectory(path);
}
WriteLog(datasInfo[i].CreatedBy.ToString());
Console.WriteLine(datasInfo[i].CreatedBy.ToString());
WriteLog(datasInfo[i].Uri.ToString());
Console.WriteLine(datasInfo[i].Uri.ToString());
WriteLog(datasInfo[i].Filename.ToString());
Console.WriteLine(datasInfo[i].Filename.ToString());
// 这里出现了很多次一场,就是那种数组越界的那种
// 不明白为什么会出现数组越界???
Console.WriteLine(i);
Task.Run(() => downs(datasInfo[i].Uri.ToString(), path + datasInfo[i].Filename.ToString()));
// downs(datasInfo[i].Uri.ToString(), path + datasInfo[i].Filename.ToString());
//路径应该设置为用户注册邮箱，设想：重新查询后，对文件夹进行重命名
}