A small problem.

[MajdMTA]

Hello there i tried to make instead of clicking "Login" pressing enter it will be logged automatic.

function clientSubmitLogin(button, state) 
    if button == "left" and state == "up" then 
        local username = guiGetText(loginEdit["Username"]) 
        local password = guiGetText(loginEdit["Password"]) 
        if username and password then 
            triggerServerEvent("submitLogin",localPlayer, username, password) 
        end 
    end 
end 
addEventHandler("onClientGUIClick", loginButton["Main"], clientSubmitLogin, false) 
bindKey ( player, "enter", "down", clientSubmitLogin ) 

[Rataj]

In client side you should not define player in function bindKey.

Try to use it like this instead:

bindKey("enter", "down", clientSubmitLogin) 

Also you need to edit condition in start of function, because it will not go through using it like this.

[Noki]

You're also checking for two states (parameters that were from the onClientGUIClick event). bindKey passes the key you hit (enter) and the state of that key (up or down). So, you will need to modify your original function to accommodate for this as well.

[KariiiM]

Btw

bindKey ( player, "enter", "down", clientSubmitLogin ) 

You're using player outside the function plus not defined and after all it's client side and there's no player argument.