Incorrectly issued certificates were a common issue in Office Communications Server deployments, but these issues should mostly be mitigated with the new Lync Server wizards. The option to manually request and modify the certificate still exists, which might lead to some problems.
Follow the following guidelines to rule out any certificate issues:
• Subject and subject alternative names—Ensure that the required subject name and subject alternative names have been entered for each role. The guidance for each role varies, so verify the names required when deploying a new server. Always use the certificate wizard suggested names if possible. Wildcard certificates are still technically unsupported for most scenarios.
• Key bit length— ...