I admit that I too would be a bit flummoxed if a witness said "No" to the standard question (at the outset of his testimony) as to whether he swore to tell the truth, the whole truth, and nothing but the truth. Who says "No" to that?!
You nonetheless gotta do better than this. Which essentially amounts to just letting it go and having the witness testify anyway.
As a result, someone sentenced to 60 years in prison for first-degree murder gets a new trial.