Dim Loop1 As Integer
 Dim TempFileName As String
 Dim MyFileCollection As HttpFileCollection = Request.Files
 
 For Loop1 = 0 To MyFileCollection.Count - 1
    ' Create a new file name.
    TempFileName = "C:\TempFiles\File_" & CStr(Loop1)
    ' Save the file.
    MyFileCollection(Loop1).SaveAs(TempFileName)
 Next Loop1

------解决方案--------------------
C# code

//请确定你的Load文件夹存在。如果不存在先创建！
if (Directory.Exists(@"D:/Load/"))
{
   Directory.CreateDirectory(@"D:/Load/");
}
//然后在保存
f.SaveAs((@"D:/Load/" +f.FileName )