According to the Wikipedia entry on Anne Frank, her father willed the copyright to the Anne Frank Foundation, with the provision that the first 80,000 Swiss francs went to his heirs; the surplus going to the works of the foundation.
http://en.wikipedia.org/wiki/Anne_Frank
(towards the bottom of the page, in the section titled, "Legacy.")
Under the circumstances, the Foundation may well not wish to give waivers for free ebooks, if they have a duty to provide for the heirs.
Also, if the translator of the original version is still alive, or recently dead (and she was alive 1n 2001) then she, or her estate, would have to waive their copyright too.
Matters are further complicated by the fact that the Anne Frank diary is not one text.
There exist:
1. her original diary.
2. The version she edited,
3. The first published version, as further edited by her father.
Montsnmags has pointed to the most recent version, which has all three texts in parallel. It looks like the most complete text available. It's unlikely to enter the public domain in Europe until 70 years after the death of the last surviving editor/translator.
You can read the editorial history of the Diary here:
http://en.wikipedia.org/wiki/The_Diary_of_a_Young_Girl
It would be good to see the Diary more widely, even freely, available. It is an enduring monument. But one also has to respect Herr Otto Frank's wishes on the matter.