Solved by myself.
1. Updated origin to latest beta version.
2. Activated hot spot shield.
3. Updated game to latest patch.
WARNING : with previous stable version of origin I could play Mass Effect 3 : multilayer (with my previous patch 1.04) but that was not possible with beta version, which kept asking to update the game. So I recommended you to complete current weekend challenge of Mass Effect 3 : MP with current version just to be safe.
