sortere gengangere fra

SELECT DISTINCT postnr FROM skoler ORDER BY postnr

den her kode:

<!--#include file="../include/protect.inc"-->
<!--#include file="../include/dbconn.inc"-->
<!--#include file="../include/levelcheck.asp"-->
<%
SQLskole = "SELECT DISTINCT postnr FROM skoler ORDER BY postnr"
set rs = Conn.Execute(SQLskole)
%>
<HTML>
<head>
<title>skolesøgning</title>

<link rel="stylesheet" href="../include/register.css">

</head>
<BODY bgcolor="#7795A5" class="text">
<!--#include file="../include/menu.inc"-->
<br>
<table border="0" cellpadding="0" cellspacing="0">
<tr>
<td class="text">
<b>
<%
if not rs.EOF then
Do While not rs.EOF
post = rs("postnr")
%>
<a href="listpost.asp?nr=<%=post %>"><%=post %></a>
<br>
<%
rs.MoveNext
    Loop
else
response.write ("Ingen skoler der har nogle postnumre")
end if
%>
</b>
</td>
</tr>
</table>
</body>
</html>
<%
Conn.Close()
Set Conn = nothing
%>
giver den her fejl:

Error Type:
Microsoft OLE DB Provider for ODBC Drivers (0x80040E14)
[Microsoft][ODBC Microsoft Access Driver] The changes you requested to the table were not successful because they would create duplicate values in the index, primary key, or relationship. Change the data in the field or fields that contain duplicate data, remove the index, or redefine the index to permit duplicate entries and try again.
/crm/skoler/listskolerpost.asp, line 6

ok det virkede hvis man bruger GROUP BY istedet for ORDER BY
jeg takker for hjælpen :)