Hi belgind,
Most likely because the submit option is still ticked (from memory multiple choice options don't untick when an error/message triggers).
May I ask why you're using a multiple choice option in place of a submit button? You'd likely have an easier time adding code to a question on that page that modifies the usual "Next" button:
jQuery("#NextButton").val('Submit');
jQuery("#NextButton").css({"width": "99%", "background-color": "#007ac0"});  //add whatever styling you want
This will behave the way you require.

Becasue I removed all "next buttons" since I am conducting time-restricted experiment. They were distracting. But your solution worked though. When I hit enter, the experiment proceed thank you!


Is there any way to proceed when participants press left and right arrows? and record which one they pressed?

Yes there is! GIve this a go
(my Qualtrics is down right now, this is untested)
//add this to the onLoad function

//detecting arrow key presses
document.addEventListener('keydown', function(e) {
//check which key was pressed
    switch (e.key) {
        case "ArrowLeft":
//set the pressed key in the embedded data - or store it however else you want
Qualtrics.SurveyEngine.setEmbeddedData("keyPressed", "Left key");
//press the next button
function () {document.getElementById('NextButton').click()}
            break;
        case "ArrowRight":
Qualtrics.SurveyEngine.setEmbeddedData("keyPressed", "Right key");
function () {document.getElementById('NextButton').click()}
            break;
    }
});
Good luck!