ASP随机产生字母怎么老是重复呢？各位帮帮忙民！源码放上!

下面源码，我制作卡到一定数量就会重复，比如我一次制20张卡，卡1,卡2,卡3,卡4,卡5，卡6,卡7,卡8,卡9,卡10...卡20,通常从卡9开始就重复卡1到卡8了，真不知是什么问题啊~~求各位帮帮忙了！！！
<%
dim shijian,shumu,kami,zaokaren
        
    shijian=request("item")
    shumu=request("shumu")
    zaokaren=request("u")
   
        rs.open "select * from kaka ",con,1,3
    for i = 1 to shumu step 1
        kaka=suijimima(32)
        rs.addnew
        rs("card")=kaka
        rs("type")=shijian
        rs("status")="未使用"
        rs("make")=zaokaren
        rs.update   
    next
        rs.close
        set rs=nothing
        response.write("制作充值卡成功")
        response.end
Function suijimima(ByVal mimaweishu)
Dim suijishu,i,ZM,k
    ZM = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    k = Len(ZM)   
    For i = 1 To mimaweishu
        Randomize
        j=Int(k * Rnd )+1
        suijimima = suijimima & Mid(ZM,j,1)
    Next
   
End Function
%>

[ 本帖最后由 kainet 于 2011-11-2 15:53 编辑 ]