I hope it happens when there is delay in the HTTP response.  We can suppress it using the error_reporting functionalists.

  var group = document.getElementsByName('groups[]');
 var groupError    =    true;
   
    for(var g = 0; g < group.length; g++)
    {
        if(group[g].checked == true)
            groupError    =    false;
    }
document.write(groupError);