While speaking with my tandem partner (Mothertongue: Austrian German) I happened to say: "Ich weiß es nicht mehr genau" and the girl told me that to her German ears that sounded wrong. She said it was too much and that I would have to say: "ich weiß nicht mehr" or "ich weiß nicht genau". Not both together in the same sentence. She could not really explain me why. She just said it sounded wrong and somehow too much.
What I was trying to say was "I don't know anymore exactly ... (bla bla bla)".
Does it sound wrong to you too? Is it maybe that I could say it but I would better not write it because it's not formal enough? Why is it wrong, by the way?
If that is really wrong, how do I express "I don't know anymore exactly ..."