The same here, not good news in the e-mail.
It's kind of annoying there is indeed no further information given about the why and how.
It blows anyway failing an interview, in my opinion.
I'd rather failed the first, second or fourth test then, since those are an objective evaluation of skills you fail or pass fair and square, rather than an interview where there's always a subjective interpretation of answers given to questions which might not even probe correctly the sought after competences.
On the other hand, I might have failed the English test, which I'd actually prefer.