While expanding a distribution list OCS user recieve the below error
Cannot synchronize with the corporate address book. This may be because the proxy server setting in your web browser does not allow access to the address book. If the problem persists, contact your system administrator.
Distribution group service could not perform this action .Contact system administrator to investigate this problem.
Case study :
The issue happened because of the internal certificate which is renewed.
I took the configuration information of the MOC client and took the internal Url entry
Eg. Internal From Server :https://ocspool.mydomain.com.com/Abs/Int/Handler.
While browsing this URL I found it was not opening. Then checked the IIS in one frontend server and checked the certificate associated to that (edit bindings-option) Select new certificate and clicked OK.
And Issue is resolved :)