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DO you have in your Enterprise Parameters the URL using thr FQDN of the CCM or the IP address? Switch to IP address to rule out DNS, also try a IISRESET from the command line of the server where the directory is homed too.
What Regions do you have configured on your call manager? Are you using G711 or g729 between those calling parties? If you are that is why, you need a transcoder.
