ssl certifictae prompt from outlook client

We setup exchange 2010 sp1 but we noticed that users who have outlook client 2007 and 2010 get prompted about ssl certificate. One is the external for the owa and then requests for the internal CAS server.  These are people who haven't been migrated yet to exchange 2010, they are still on exchange 2003.  I noticed even those that have been migrated, some were prompted but it went away.  Not sure what is going on with this.  Has anyone run into this issue.  
hbpubAsked:
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RubenAtDKCommented:
you should bye a UC certificate containing your external URL for OWA, autodiscover Active-sync etc. and your internal FQDN, and hostname, and the Exchange 2003 FQDN, if you plan for coexistens.

ex.:

OWA.COMPANY.COM
AUTODISCOVER.COMPANY.COM
SERVER.DOMAIN.LOCAL
SERVER
EX2003.COMPANY.COM
(you only need the ex2003 external FQDN if you put the FQDN in you internal DNS.)

use the certificate wizard in EMC.
endital1097Commented:
no matter what version of exchange you have, outlook 2007 and higher will always have autodiscover attempt to detect configuration settings
once you introduce the first exchange 2007/2010 server you now have a scp for autodiscover and outlook will attempt to obtain its configuration settings

take a look at this article for configuration of the 2010 server
http://www.experts-exchange.com/Software/Server_Software/Email_Servers/Exchange/A_3704-Troubleshooting-Outlook-Certificate-Errors.html

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ash007Commented:
you dont need to have UCC certificate for internal outlook clients
refer artilce-kb-940726 & change urls for Autodiscover,OAB,EWS virtual directories
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