During synchronization, changes are reconciled and posted into the replica version. A failure has occurred during this reconciliation. One of the reasons this could occur is if another operation locked the replica version while attempting to synchronize. If the reconciliation fails, the replica will be listed as in conflict. You can use the replica manager to determine whether a replica is in conflict.
To resolve this, you should take the replica out of conflict. See Resolving synchronization conflicts manually for more information.