What is the easiest way to undo a posted customer payment and get the amount due back into receivables?

THAT WAS HELPFUL INFO.... THANKS :

Yes, we had a problem this week.  A new person took matters into their own hands and posted payments.  Unfortunately, it was wrong.  The check was for 2 invoices and 1 credit.  She posted each invoice separately for the full amount of the invoice using the same check #, then could not post the credit amount.  When we tried to reverse the check, we could not since there were two payments on the same day for the same check #.  
 
I had to create another invoice (voucher) charging our undeposited checks account, then posted a -0- dollar payment, selecting the credit memo & newly created voucher.
 
I always hate when A/R payments are incorrectly handled, they are so hard to correct.

Well in my case it was one payment to the undeposited funds account (instead of the checking account).  It would not let us reverse it.  Period end of sentence.
 
I thought DBA was user friendly.... hummmm I better check that fine print again.

Something to the effect that that date was already used try another date.
 
I had two users yesterday both experience problems reversing payments.  But here's a another question... does it matter if your original payment has been GL-O posted before you try to reverse it?

Well I thought maybe that was the problem.. OH WELL.. maybe it was the bitter cold Montana weather.

It may be a problem with the report. Is the Aging correct and in balance with the GL?  
 
There was a problem with the AR Payment report showing reversals incorrectly. I don't know if its been fixed or not (haven't needed to do a reversal in awhile). Also might depend on which version you're on.