求高手点错。这个asp添加用户的代码块。出错（服务器维护中）

username=Trim(Request("username"))
set rs=server.createobject("adodb.recordset")
sql="select * from admin where username='"&username&"'"
rs.open sql,conn,1,1
if rs.recordcount<>0 then
response.write "<script language=JavaScript>" & chr(13) & "alert('该用户名已存在,请重新输入！');" & "history.back()" & "</script>"
Response.End
else
rs.AddNew rs("username")=Trim(Request("username"))
rs("name")=Trim(Request("name"))
rs("password")=Trim(Request("password"))
rs("leixing")=Request("leixing")
rs.Update
response.write ("<Script Language=Javascript>window.alert('用户添加成功！');location.href='user_admin.asp';</Script>")
rs.close
set rs=nothing
set conn=nothing
end if
%>