Okay let me try and translate this in English - I'm guessing that you have to use 0,1 out of 0,15 keyboard keys to make anything work so
elseif isbuttonpressed(6,0) then
PedSetActionNode(GPlayer,"/Global/P_Striker_A/Defense/Evade/EvadeCounter/LightAttacks/EvadeBackPunch","Act/Anim/P_Striker_A.act")
end