使用Adodb.Stream下载文件(如下代码)。

       Response.ContentType = "application/octet-stream"
       response.AddHeader "Content-Disposition","attachment;filename=" &  objRs("Attach_Name")& filetype
       Set Stream = Server.CreateObject("ADODB.Stream")

       Stream.type=1
       Stream.Open
       Stream.LoadFromFile server.mappath(objRs("Attach_path"))
       Response.BinaryWrite Stream.Read         
       Stream.Close
       Set Stream = Nothing

当下载文件小于4M时没问题，大于4M时出错，提示 ：

Response对象错误 'ASP 0251 : 80004005'     
    
超过响应缓冲区限制

问题出在IIS的配制中AspBufferingLimit只有4M，所以有如下几种解决办法：

1、修改IIS的配制

停止IIS服务，然后用记事本修改C:\WINDOWS\system32\inetsrv\MetaBase.xml   
  中的:   
   AspBufferingLimit="4194304"    //即默认4M   
  改为:   
   AspBufferingLimit="8388608"    //改为8M或更多，自己决定

2、如果不想修改IIS的默认配制就要修改代码了。

     Response.Buffer=False   ‘将Response.Buffer设为否
     Response.ContentType = "application/octet-stream"
       response.AddHeader "Content-Disposition","attachment;filename=" &  objRs("Attach_Name")& filetype
       Set Stream = Server.CreateObject("ADODB.Stream")

       Stream.type=1
       Stream.Open
       Stream.LoadFromFile server.mappath(objRs("Attach_path"))
     offset = 0
     ChunkSize = 2048*1024        ‘ChunkSize小于IIS配制文件中的AspBufferingLimit项所设置的大小
     TotalSize = Stream.Size
     while offset < TotalSize
         if (TotalSize - offset < ChunkSize) then
             ChunkSize = TotalSize – offset
         end if
         strChunk = Stream.Read(ChunkSize)         
            Response.BinaryWrite strChunk       
          offset = offset + ChunkSize
     wend        
       Stream.Close

或者

Response.Buffer= true     ‘使用缓冲区
    Response.Clear                
   Response.ContentType = "application/octet-stream"
       response.AddHeader "Content-Disposition","attachment;filename=" &  objRs("Attach_Name")& filetype
       Set Stream = Server.CreateObject("ADODB.Stream")

       Stream.type=1
       Stream.Open
       Stream.LoadFromFile server.mappath(objRs("Attach_path"))
     offset = 0
     ChunkSize = 2048*1024
     TotalSize = Stream.Size
     while offset < TotalSize
         if (TotalSize - offset < ChunkSize) then
             ChunkSize = TotalSize – offset
         end if
         strChunk = Stream.Read(ChunkSize)         
            Response.BinaryWrite strChunk       
            response.flush                ‘这句很重要，它把缓冲区的数据据推出去
          offset = offset + ChunkSize
     wend        
       Stream.Close