这是我的代码（无组件上传），变量filepath没错，用response.binarywrite能够完整显示文件名称，但是用函数binarytostring转换成字符串的时候报错

Microsoft VBScript 运行时错误 错误 '800a000d'

类型不匹配: 'binarytostring'
<%
dim formdata,formsize
formsize=request.totalbytes
formdata=request.BinaryRead(formsize)
dim filepath,contenttype,fileimage,filesize
dim bncrlf,divider,datastart,dataend,datalen,temp
bncrlf=chrb(13)&chrb(10)
divider=leftb(formdata,cint(instrb(formdata,bncrlf))-1)
datastart=instrb(formdata,bncrlf)+57
response.Write datastart&"开始"
dataend=instrb(datastart,formdata,bncrlf)-1
response.Write dataend&"结束"&"</br>"
datalen=dataend-datastart
filepath=midb(formdata,datastart,datalen)
binarytostring (filepath)
%>

请各位给指点一下，调试环境iis7+windows7