Certificate-based VDFS replication may halt when the replication certificate expires. The following note will be displayed on the Replication tab in the VisualSVN Server Properties:
The following error is logged to the VisualSVN Server Replication event log on the master server:
The replication certificates installed on master and slave servers must be valid and not expired for the VDFS replication to work over certificate-based authentication. When the replication certificate expires it becomes invalid.
The expired certificate should be replaced with a valid and trusted certificate. For further information, read the article KB121: Understanding Replication Certificates.