Week 3 Exercise 6 (backward propagation)

Right, exactly as you reported. I think that I am correct to assume that all preceding functions have passed their tests, in which case the best that I have to offer is that you check and recheck your expressions for the gradient. Also be sure that you have not accidently changed other parts of the function. If you no longer have the original copy available as a reference, you can download as fresh one using this FAQ.