Communicator troubleshooting

I had a weird issue which occured at the communicator client (R2). The OCS (Office Communication Server) is version 2007 R2.

When I logged in (internal), the client had an exclamation mark. The following 2 errors occured :

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.

Communicator could not retrieve calendar or Out of Office information from Exchange Web Services. Communicator will automatically  continue to retry. If this problem persists, contact your  system administrator.

When I started troubleshooting the issue I also noticed that Read more »