I don't understand why you would be getting this error, it is coming from your confirm page at line 5. According to the error it seems that there is some output occurring on line 5. What is the code that you have on line 5 of the confirm page? Please post back with a current copy.
It seems strange that you would get this error because you were not getting this error previously. It was failing the transaction before, so it would have to be able to load this page without this error.