duplicate bill

Hi. I am trying to sort out the trial balance and have been going through bills to check if any were paid before they were issued (if that makes any sense). Anyway, I have found a duplicate bill ie: it is in the system twice and has registered paynebnt twice. I tried to delete one but myob is telling me I can't delete a bill which has a payment ahgainst it. How can I delete this extra bill?

Cheers

kefa