Thank you NK. This particular error 1203 means that an UPDATE or DELETE was performed at source and when the replicat tried to replicate that change in the target table, it couldn't find that row. Right ?
Network outage or server outage could be one of the reason for the Target not to be in sync. But once the network/server issues are fixed the 'pending' changes will be applied . So, how could the target become out of sync ?