Hi,
Following this french article (www.mathdax.ca/.../dynamics-ax-2012-license-information.html) I solved this issue.
Run process monitor while you try to start you AOS service. Find the last entry related to ax32serv.exe, for me it was access denied on a key in the folder C:\ProgramData\Microsoft\Crypto\RSA\MachineKeys.
I modified the rights on it to grant my service account running the AOS service "Read and Execute". And it worked !
However I don't know what it imply for the future of my AOS service..