Problem for Bill : Can't delete bills

Hi, I'm having issues deleting bills for some reason. It doesn't delete when I push delete. Also, when I add payment to the bill, it shows up as a partially paid and it doesn't show as paid. This creates problem.
I've encountered this problem ever since the software was updated.
Is it a part of bug problem? Does anyone have a same issue?
If I could get some help here, that'll be great.