Hi,
Thanks you for the tips 
Here some lines of the log file (all LogOnline):
[2015.07.23-18.35.40:863] 0]Log file open, 07/23/15 20:35:40
[2015.07.23-18.35.40:863] 0]LogEngine:Display: Android Version Make Model Language: 2.3.7 Sony Ericsson ST25i it_IT
[2015.07.23-18.35.40:863] 0]LogAndroid: Case APP_CMD_START
[2015.07.23-18.35.40:863] 0]LogAndroid: Case APP_CMD_RESUME
[2015.07.23-18.35.40:863] 0]LogInit:Display: Running engine for game...
...
...
[2015.07.23-18.35.40:867] 0]LogOnline:Display: OnlineSubsystemGooglePlayModule::StartupModule()
[2015.07.23-18.35.40:867] 0]LogOnline:Display: FOnlineIdentityAndroid::FOnlineIdentityAndroid()
[2015.07.23-18.35.40:867] 0]LogOnline:Display: FOnlineStoreGooglePlay::FOnlineStoreGooglePlay
[2015.07.23-18.35.40:867] 0]LogOnline: GPG sign in started
[2015.07.23-18.35.40:867] 0]LogOnline: FOnlineSubsystemGooglePlay::OnAuthActionFinished, Op: SIGN IN, Status: VALID
[2015.07.23-18.35.40:867] 0]LogOnline: Async task 'Login' completed in 2.364990 seconds with 1
...
...
[2015.07.23-18.35.42:873] 0]LogOnline:Display: FOnlineIdentityAndroid::GetPlayerNickname
[2015.07.23-18.35.43:230] 0]LogInit:Display: Game Engine Initialized.
...
...
[2015.07.23-18.35.51:745] 0]LogOnline:Display: FOnlineIdentityAndroid::GetPlayerNickname
[2015.07.23-18.35.52:447] 0]LogOnline:Warning: GetLeaderboardID: No mapping for leaderboard Score
...
...
[2015.07.23-18.35.57:776] 0]LogOnline:Warning: Async task 'ReadLeaderboard' completed in 5.175354 seconds with 0
[2015.07.23-18.35.59:474] 0]LogOnline:Display: OSS: WriteLeaderboards
[2015.07.23-18.35.59:481] 0]LogOnline:Display: OSS: Going through
Here is the DefaultEngine.ini mapping for the score leaderBoard
Thanks Again for your tips and support
Best regards
Stéphane