Well it's telling what the problems is. An attempt is being made to update a row at a subscriber and it is not there. Sounds like error 20598 to me.
You can either set the agent to ignore this error, but this leads to data inconsistency.
Another option would be to manually insert the missing row into the subscriber. This would mean looking into the distribution database to find the record. But as a DBA i'm sure you are up to this.
You might want to investigate what has caused the data inconsistency