This is a negative question and one that wherever possible should be avoided. It does not matter how you answer the question, the answer you give will have to result in you providing the interviewer with evidence of a negative point. Wit this in mind it is worth trying to avoid answering the question at all if you can although this again can raise a negative point if it can be shown that you failed to provide an answer. If there is something positive that you are able to dress up as a negative then perhaps that might be the way to do it.
Examples of Answers
“When I was a junior manager in my first role following university I was given a research project to undertake for the company to identify a new technique for a manufacturing process. As there was little work to do at the time apart from this project I spent considerable hours looking into the problem and came up with what I thought was the perfect solution.
I presented this to senior management who were very impressed by the findings but unfortunately the situation at the time with the strength of the unions within the company determined that the process I had developed could not be implemented as it would negatively impact on the workforce. I was vindicated many years later when union power waned at that plant and the process I had come up with many years beforehand was duly implemented. So although I failed to sell the idea at the time it was because the political situation within the company was wrong for implementation.”