Error When Unposting an Account.

Hello,

I am trying to assist my User with the Error message she was getting when trying to UNPOST a payment that was posted to the wrong invoice number.

she can  unpost the payment, but I can't repost the payment with the TYPE as PY.

she is getting the  error Message : You may not Select Payment or Write Off Item Entry Type for a new Item(6040,590)

User has Posted it to the wrong customer

Accounts receivable, receivables update, unpost groups, Payment group, 
Inputed the deposit ID and selected the item they wanted
They then clicked on one of the tabs and input the reason for "wrong invoice".