euca-add-keypair not generating keys on CentOS 6

Hello,
I installed OpenStack Diablo on a CentOS 6. I can run an instance and I can ping it.
My problem is when creating key pair using "euca-add-keypair" ("euca-add-keypair mykey" for ex), I always get error "UnknownError: An unknown error has occurred. Please try your request again."
When I look in logs "/var/log/nova/nova-api.log", I can see :

2011-11-02 17:29:41,283 nova.api: action: CreateKeyPair
2011-11-02 17:29:41,284 nova.api: arg: KeyName val: mykey
2011-11-02 17:29:41,290 nova.utils: Running cmd (subprocess): ssh-keygen -q -b 1024 -N -f /tmp/tmphO9Q8u/temp
2011-11-02 17:29:41,380 nova.utils: Result was 1

It seems that the passphrase is not passed to ssh-keygen.
Anyone has ever had this issue?