While many PingDataSync issues are deployment-related and are directly affected by the hardware, software, and network structure used in the synchronization topology, most failures usually fall into one of the following categories:

Entry Already Exists
When an add operation was attempted on the destination server, an entry with the same DN already exists.
No Match Found
A match was not found at the destination based on the current Sync Classes and correlation rules (DN and attribute mapping). When this value has a high count, correlation rule problems are likely.
Failure at Resource
Indicates that some other error happened during the synchronization process that does not fall into the first two categories. Typically, these errors are communication problems with a source or destination server.

Statistics for these and other types of errors are kept in the cn=monitor branch and can be viewed directly using the status command.