Communicator cannot determine the location of the Exchange Web Service

Solution:

Exchange 2007 sp1 server sets the exchange web services required by the host Outlook 2007 client and the OC 2007 client. One of them is called autodiscover service, which is run in IIS 2007 on the exchange 6.0 server as a virtual application. The Outlook 2007 and communicator 2007 clients connect to this autodiscover virtual application to discover available service URLs of Exchange 2007. This connection is connected through port 443 and requires 128-bit encryption. If the certificate of IIS 2007 default website applied to the exchange 6.0 server is not installed, you will receive the error message you described. This issue should not occur in the configuration combination of ol 2003/Exchange 2003 or ol 2003/exchange 2007.To solve this problem, we need to confirm that the correct certificate has been installed on Exchange 2007/IIS server. perform the following steps to check:
1. Open IIS manager on the Exchange 2007 server and locate the default website.
2. Open the properties for the default website and activate the Directory Security Tab
3. Click on view certificate and make sure that a Web server certificate is installed on the default website that meets the requirements listed below.

A. It shoshould have a subject name that is the FQDN of the Exchange 2007 Server
B. It shoshould have an enhanced Key Usage Value of Server Authentication OID 1.3.6.1.5.5.7.3.1
C. It shoshould have certification path to the certificate authority that is hosting the certificate authority certificate for the ol 2007 client.

4. if the customer is using a public ca e. g. veriSign to acquire their certificates then they will need to purchase one for the Exchange 2007 server. if they are using a Windows PKI to manage certificates then find out if they have a domain certificate auto-enrollment policy enabled that supplies the computer (machine template) certificate. if necessary the customer can use the Windows PKI to manually issue a web server certificate to the Exchange 2007 server.
5. when Exchange 2007 is installed on a Windows server it will install a self signed certificate that has the subject name of the single label name for the Exchange 2007 server. this certificate is not sufficient for the HTTPS connectivity that is needed for the Windows client connectivity to the Exchange 2007 WebServices.

Generally, you only need to apply for a new certificate from the Root CA.