Pop Up messages on screen

Just upgraded from ASPRunner 6.0 to 6.3
With the previous version I often displayed pop up message boxes on the screen such as in the example below:
if Dict("EDC") > "" and Dict("EDC") < date Then
%>

<script language="JavaScript" type="text/javascript">alert("EDC must be greater than today's date")</script>

<%
BeforeEdit = False
end if
This code does not work with 6.3.
Is there an alternative way of displaying messages to the users to replace the Javascript alert function