Follow this post if the solution published on my blog dated 16th April 2009 is not working.
If making changes to default-web-site.xml file does not work, then try to change an entry in the server.xml file. The file is located under:
Note: Stop the server before making any changes to the server files.
In the file, change the below property to true:
application name="ascontrol" path="../../home/applications/ascontrol.ear" parent="system" start="true" /
Now start the SOA Server and try launching the enterprise manager. You should be able to see the AS control page now.