如何会错了

怎么会错了?
<%
if   session( "userid ")= " "   then
Response.Write   " <Script> alert( '请先登陆，再进行此项操作! ');navigate( " "index.asp " ") </Script> "
response.end

end   if

%>

不登陆提示出错，可是我登陆了设置了session( "userid ") <> " "   怎么再打开这个页面还提示这个 "请先登陆，再进行此项操作 "

------解决方案--------------------
<%
Response.Write session( "userid ") & "---Session " '看看session( "userid ")的值是什么
Response.End
if session( "userid ")= " " then
Response.Write " <Script> alert( '请先登陆，再进行此项操作! ');navigate( " "index.asp " ") </Script> "
response.end

end if

%>


单凭这段代码看不出来什么？