This error is encountered when the replica from which you are trying to synchronize edits is already in conflict.
To move past this error, you need to resolve the conflicts on the replica. While conflicts exist, you will be able to synchronize to get changes, but you will not be able to send changes. Use the replica manager to determine if a replica is in conflict. See Resolving synchronization conflicts manually for more information on how to resolve these conflicts. See Synchronization and versioning to learn more about how geodatabase replication uses versioning during the synchronization process.