ICSharpCode.SharpZipLib.Zip.ZipException: EOF in header

//异常提示：ICSharpCode.SharpZipLib.Zip.ZipException: EOF in header 

NPOIMemoryStream stream = new NPOIMemoryStream();
using (var fileStream = File.Open(filePath, FileMode.Open, FileAccess.ReadWrite))
{
    fileStream.CopyTo(stream);
    stream.Position = 0; //这一句不加就会上面的异常错误
}
IWorkbook wk = new NPOI.XSSF.UserModel.XSSFWorkbook(stream);

 还有种情况报这个错误，NPOI打开了空的流对象，这种情况NPOI不用传流对象创建IWorkbook对象，直接调用无参构造函数，最后操作完之后将结果写入到流中；最后提示一下：写入流之前也需要 stream.Position = 0;

protected IWorkbook GetWorkbook(string ext)
{
    IWorkbook book = null;
    if (ext.ToLower().Equals(".xls"))
    {
        book = new HSSFWorkbook();
    }
    else if (ext.ToLower().Equals(".xlsx"))
    {
        book = new NPOI.XSSF.UserModel.XSSFWorkbook();
    }
    else
    {
        throw new SinoException("只支持Excel文件");
    }
    return book;
}

打开Excel文件流的方式

protected IWorkbook OpenWorkbook(Stream stream, string ext)
{
    IWorkbook book = null;
    if (ext.ToLower().Equals(".xls"))
    {
        book = new HSSFWorkbook(stream);
    }
    else if (ext.ToLower().Equals(".xlsx"))
    {
        book = new NPOI.XSSF.UserModel.XSSFWorkbook(stream);
    }
    else
    {
        throw new SinoException("只支持Excel文件");
    }
    return book;
}

  public class NPOIMemoryStream : MemoryStream
  {
        /// <summary>
        /// 获取流是否关闭
        /// </summary>
        public bool IsColse
        {
            get;
            private set;
        }
        public NPOIMemoryStream(bool colse = false)
        {
            IsColse = colse;
        }
        public override void Close()
        {
            if (IsColse)
            {
                base.Close();
            }
        }
  }