I approved a bill.  I then wanted to un-approve it in order to make some corrections to the slips on that bill. I went to "approved" bills, and clicked to clear the bill.  After that, the bill no longer shows as an approved bill, but the slips that had been in the bill still show as "billed" and are locked so that I cannot edit them or put them in a new bill.  When I go to generate a new bill, it simply issues a statement showing the amount due on the bill that I thought I had already cleared.  How can I fully clear the slips so that they no longer indicate they have already been billed.  Thank you.