I have done my period end and year end. I only now noticed that there are Posting errors in the previous year that I need to delete. How do I do that when I can't get back into the previous year to unpost a particular batch?

You will need to create a batch of adjusting errors and post it to the prior period (year).

I just noticed your other post. Is this issue the same and/or does this issue refer to accounts payable or general ledger?