I am investigating such an error right now (see my new post at Statutory Records). I discovered I can't PROVE the parentage of my gggg grandfather. If his parents aren't who I have listed, there will be a whole lot of trimming to be done, as I have gone up and down side branches.
I have found a man and wife of the same surname and forenames on the 1841 census. If those two are mine, it means that my gggg grandfather didn't die in 1862 with the parents I have listed, which I received from a distant cousin who, when questioned much later, couldn't recall how she arrived at them! All it will take is finding out census man's wife's surname...if it is McCouat (var.) then I am sunk and will have to delete a lot!
Still, the research was a lot of fun. And I will have a ready made, well researched tree for someone else one day!
Nina