Hi
If the PO is already vouchered you must reverse the voucher first, then you will be able to reverse the receipt. Then the PO will be open and you can enter in PO detail and cancel the lines.
To reverse a voucher do from P0411, to reverse a receipt do from P43214 this is a bit tricky, follow this steps.
1. be sure that you have the voucher reversed.
2. enter P43214 and query for the OV you want to reverse
3. select the line and check in the row exit for Journal Entries (6 button from the top) to look for the GL date, and close this screen
4. enter the GL date to be used to post the reverse batch in the form field GL Date
5. select again the line and click the row exit reverse receipt.
6. exit the screen
HTH
