javascript IE bug

Hello, this is my first post here. I have encountered sth strange on my website. Every menu item is working fine except 3rd one, this is only IE problem.

JS code:
[LEFT]switch (str) {
case ‘main’: {
document.getElementById(‘a_home’).className=”active”;
document.getElementById(‘a_about_us’).className=””;
document.getElementById(‘a_team’).className=””;
document.getElementById(‘a_services’).className=””;
document.getElementById(‘a_contact’).className=””;

break;
}
case ‘about_us’: {
document.getElementById(‘a_about_us’).className=”active”;
document.getElementById(‘a_home’).className=””;
document.getElementById(‘a_team’).className=””;
document.getElementById(‘a_services’).className=””;
document.getElementById(‘a_contact’).className=””;

break;
}
case ‘team’: {
document.getElementById(‘a_home’).className=””;
document.getElementById(‘a_about_us’).className=””;
document.getElementById(‘a_team’).className=”active”;
document.getElementById(‘a_services’).className=””;
document.getElementById(‘a_contact’).className=””;
break;
}
case ‘services’: {
document.getElementById(‘a_services’).className=”active”;
document.getElementById(‘a_home’).className=””;
document.getElementById(‘a_about_us’).className=””;
document.getElementById(‘a_team’).className=””;
document.getElementById(‘a_contact’).className=””;
break;
}
case ‘contact’: {
document.getElementById(‘a_contact’).className=”active”;
document.getElementById(‘a_home’).className=””;
document.getElementById(‘a_about_us’).className=””;
document.getElementById(‘a_team’).className=””;
document.getElementById(‘a_services’).className=””;
break;
}
default: document.getElementById(‘a_’+str).className=””;
}[/LEFT]

I know this switch isnt the greatest solution for navigation, but i couldnt figure out anything better sice im kinda new to js ?

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