<%
   if IsEmpty(Session("Passed")) then
        Session("Passed")=False  
    End if
    if Session("Passed")=False then
      username=Trim(Request.Form("username"))
      password=Request.Form("password")
      if username="" or password="" then
           Errmsg="请输入用户名和密码"
    Else
         if not IsNumeric(Request.Form("confirm")) Then
                  Response.Write"<script>alert('你输入的验证码为非数字!');</script>"
                  Response.End
        End if
        if (int(Session("CheckCode")))=int(Request.Form("confirm")) then
                set rs=server.CreateObject("adodb.recordset")
                sql="select * from People where username='"&username& "'"     
                rs.open sql,conn,1,3
                if rs.EOF then
                     Emrrsg="用户不存在"
                     conn.Colse
                     Set conn=nothing
                Else
                     if md5("password")<>rs.Fields("password") then
                        Emrrsg="密码不正确"
                          conn.Close
                         Set conn=nothing
                    Else
                        Emrrsg=""
                        Session("Passed")=True
                        Session("username")=rs.Fields("username")
                        Session("Id")=rs.Fields("Id")
                         end if
                    end if
                else
                      Emrrsg="验证码输入错误！"   
                    end if
                end if
            end if
        if not Session("Passed")  then
%>

错误类型：
Microsoft JET Database Engine (0x80040E10)
至少一个参数没有被指定值。

最大的问题就是逻辑混乱，不推荐这样写IF语句。

那么应该怎么改呢？谢谢看着学习呢？

改你的代码后是这样，但不推荐你这样写代码，太乱了：

<%
if IsEmpty(Session("Passed")) then
   Session("Passed")=False  
End if

if Session("Passed")=False then
   username=Trim(Request.Form("username"))
   password=Request.Form("password")
   
   if username="" or password="" then
      Errmsg="请输入用户名和密码"
   Else

      if not IsNumeric(Request.Form("confirm")) Then
         Response.Write"<script>alert('你输入的验证码为非数字!');</script>"
         Response.End
      End if
      
      if (int(Session("CheckCode")))=int(Request.Form("confirm")) then
         set rs=conn.execute("select top 1 * from People where username='"&username& "'")
         
         if rs.EOF then
            Emrrsg="用户不存在"
            conn.Colse
            Set conn=nothing
         Else
            if md5(password)<>rs.Fields("password") then
               Emrrsg="密码不正确"
               conn.Close
               Set conn=nothing
            Else
                Emrrsg=""
                Session("Passed")=True
                Session("username")=rs.Fields("username")
                Session("Id")=rs.Fields("Id")
            end if
         end if
      else
         Emrrsg="验证码输入错误！"   
      end if
   end if
end if
%>

<script language="javascript">
<%
   Dim ReFalse, username,password,rsVerify
   ReFalse=True
   username=Trim(Request.Form("username"))
   password=Request.Form("password")
   set rsVerify=server.CreateObject("adodb.recordset")
   sql="select * from People where username='"&username& "'"     
   rsVerify.open sql,conn,1,1
   With Response
            if IsEmpty(Session("Passed")) then
               ReFalse=False     
           End if
          IF ReFalse Then
              if username="" or password="" then
                  .Write "alert('请输入用户名和密码');"
                 ReFalse=False
              End IF
          End IF
          IF ReFalse Then
              if not IsNumeric(Request.Form("confirm")) then
                  .Write "alert('你输入的验证码为非数字!');"
                 ReFalse=False
              End IF
          End IF
          IF ReFalse Then
              if Cint(Session("CheckCode")))=Cint(Request.Form("confirm") then
                  .Write "alert('验证码输入错误');"
                 ReFalse=False
              End IF
          End IF
          IF ReFalse Then
              if rsVerify.EOF then
                  .Write "alert('用户不存在);"
                 ReFalse=False
              End IF
          End IF
          IF ReFalse Then
              if md5("password")<>rsVerify.Fields("password")  then
                  .Write "alert('密码不正确');"
                 ReFalse=False
              End IF
          End IF
           IF ReFalse Then
                Session("Passed")=True
                Session("username")=rsVerify.Fields("username")
                Session("Id")=rsVerify.Fields("Id")
          End IF
           rsVerify.close
           conn.Close
           Set rsVerify=Nothing
           Set conn=nothing   
   End With
%>
</script>

<%
Dim username,password,confirm

if IsEmpty(Session("Passed")) then
   Session("Passed")=False  
End if

if Session("Passed")=False then
   username =Trim(Request.Form("username"))
   password =Trim(Request.Form("password"))
   confirm  =Request.Form("confirm")

   if username="" or password="" or confirm=""  then
      Response.Write"<script>alert('请输入用户名、密码和验证码！');history.back();</script>"
      Response.End  
   end if

   if (not IsNumeric(confirm)) or (Clng(Session("CheckCode"))<>Clng(confirm)) Then
      Response.Write"<script>alert('你正确输入验证码!');history.back();</script>"
      Response.End
   End if

   set rs=conn.execute("select top 1 * from People where username='"&username& "'")
         
   if rs.Bof and rs.EOF then
      Response.Write"<script>alert('输入的用户名或密码不正确，请重新输入!');history.back();</script>"
      Response.End
   end if  

   if md5(password)<>trim(rs("password")) then
      Response.Write"<script>alert('输入的用户名或密码不正确，请重新输入!');history.back();</script>"
      Response.End
   end if            

   Session("Passed")=True
   Session("username")=rs.Fields("username")
   Session("Id")=rs.Fields("Id")
end if

Conn.Close
Set Conn=nothing
%>

错误类型：Microsoft JET Database Engine (0x80040E10)至少一个参数没有被指定值。
 还是这个问题呢？到底是怎么回事呢？谢谢！！