无法读取上传的 excel 文件

您好，我正在尝试上传一个 excel 文件并将上传的 excel 工作表中的数据读取到另一个 excel 工作表，但我收到文件不可用错误。有人可以帮忙吗？

string filetest1;

protected void UploadButton_Click(object sender, EventArgs e)
    {
       if (FileUpload1.HasFile)
           SaveFile(FileUpload1.PostedFile);
        else
            UploadStatusLabel1.Text = "You did not specify a file to upload.";
    }
        void SaveFile(HttpPostedFile file)
        {
            string savePath = "c:''Users''*****''Desktop''";
        // Get the name of the file to upload.
        string fileName = file.FileName;
        // Create the path and file name to check for duplicates.
        string pathToCheck = savePath + fileName;
        // Create a temporary file name to use for checking duplicates.
        string tempfileName = "";
        // Check to see if a file already exists with the
        // same name as the file to upload.        
        if (System.IO.File.Exists(pathToCheck))
        {
            int counter = 2;
            while (System.IO.File.Exists(pathToCheck))
            {
                // if a file with this name already exists,
                // prefix the filename with a number.
                tempfileName = counter.ToString() + fileName;
                pathToCheck = savePath + tempfileName;
                counter++;
            }
            fileName = tempfileName;
            // Notify the user that the file name was changed.
            UploadStatusLabel1.Text = "A file with the same name already exists." +
                "<br />Your file was saved as " + fileName;
        }
        else
        {
            // Notify the user that the file was saved successfully.
            UploadStatusLabel1.Text = "Your file was uploaded successfully.";
        }
        // Append the name of the file to upload to the path.
        savePath += fileName;
        filetest1 = fileName;
        MessageBox.Show(filetest1);
        // Call the SaveAs method to save the uploaded
        // file to the specified directory.
        file.SaveAs(savePath);
   }
   protected void Compare_Click(object sender, EventArgs e)
    {
        string filetest1 = FileUpload1.PostedFile.FileName;
        **MessageBox.Show(filetest1);**
    -------------
    obook = oAPP.Workbooks.Open(filetest1); 
}

有 2 个消息框，第一个消息框返回

上传文件的名称，但第二个消息框返回空消息框