My philosophy to fixing any error is to just reverse what you did wrong in the first place. So for the AR Cash batch you will want to replicate it using the same dates in error (so that sounds like 1998) and using negative dollar amounts.
When you retrieve this to Ledger you will now have two batches with 1998 dates (one should be the perfect opposite of the other). You can either delete both or change the fiscal period from 99 to the current period and post both. I prefer to post both as this is a better audit trail.