I have a Java Script quiz I downloaded for a basic website, but I get some errors in IE but not in Chrome. How can I prevent these errors because all my users will use IE?

The error states in IE

http://www.kill-zone.com/error.png


The file structure I have is two files
js/external/mootools-core-1.4.5-minified.js
js/dg-quiz-maker.js
Admissionsprocess.html


Admissionsprocess.html
Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>

<title>Admission Process Quiz</title>
<script type="text/javascript" src="js/external/mootools-core-1.4.5-minified.js"></script>
<script type="text/javascript" src="js/dg-quiz-maker.js"></script>
<style type="text/css">
body {
	font-family: 'Trebuchet MS', 'Helvetica'
}

.dg-question-label{ /* Question label */
	font-weight:bold;
}

img{
	border:0px;
}
#error {
	font-style:italic;
	color:red;
}
</style>
</head>
<body>

<center><img src="https://www.fieldsresearch.com/media/hhcahps/vision.gif"></center><p>

<?
include($_SERVER['DOCUMENT_ROOT']."/config/clicksor_760.php");
?>


<div id="questions"></div>
<div id="error"></div>
<div id="result"></div>

<script type="text/javascript">

function showWrongAnswer(){
    document.id('error').set('html', 'Wrong answer, Please try again');
}

function showScore() {
	var score = quizMaker.getScore();

	var el = new Element('h3');
	el.set('html', 'Thank you!');
    document.id('result').adopt(el);

	el = new Element('h4');
	el.set('html', 'Score: ' + score.numCorrectAnswers + ' of ' + score.numQuestions);
    document.id('result').adopt(el);

	if(score.incorrectAnswers.length > 0) {
		el = new Element('h4');
		el.set('html', 'Incorrect answers:');
        document.id('result').adopt(el);

		for(var i=0;i<score.incorrectAnswers.length;i++) {
			var incorrectAnswer = score.incorrectAnswers[i];
			el = new Element('div');
			el.set('html', '<b>' +  incorrectAnswer.questionNumber + ': ' + incorrectAnswer.label + '</b>');
			document.id('result').adopt(el);

			el = new Element('div');
			el.set('html', 'Correct answer : ' + incorrectAnswer.correctAnswer);
            document.id('result').adopt(el);
			el = new Element('div');
			el.set('html', 'Your answer : ' + incorrectAnswer.userAnswer);
            document.id('result').adopt(el);

		}
	}

}

var questions = [
	{
		label : 'What is the last step when entering an admission?',
		options : ['Assign bed', 'Enter resident name and date of birth', 'Assign organization','None of the above'],
		answer : ['Assign bed'],
		forceAnswer : true
    },
	{
		label : 'What widget is used to enter new admissions?',
		options : ['Favorites', 'Recent Admissions', 'Processes','None of the above'],
		answer : ['Processes']
    },
	

]

function showAnswerAlert() {
	document.id('error').set('html', 'You have to answer before you continue to the next question');
}
function clearErrorBox() {
    document.id('error').set('html','');
}
var quizMaker = new DG.QuizMaker({
	questions : questions,
	el : 'questions',
    forceCorrectAnswer:false,
	listeners : {
		'finish' : showScore,
		'missinganswer' : showAnswerAlert,
		'sendanswer' : clearErrorBox,
        'wrongAnswer' : showWrongAnswer
	}
});
quizMaker.start();



</script>

</body>
</html>


dg-qui-maker.js
Code:
if(!window.DG) {
	window.DG = {};
};

DG.QuizMaker = new Class( {
	Extends : Events,

	validEvents : ['start','sendanswer', 'correctanswer','wronganswer', 'finish','missinganswer','wrongAnswer'],

	config: {
		seconds: null,
		forceAnswer : false
	},

	html : {
		el : null
	},

	internal : {
		questionIndex : 0,
		questions : null,
		labelAnswerButton : 'Answer'
	},

	user : {
		answers : []
	},

	forceCorrectAnswer:false,

	initialize : function(config) {
		if(config.el) {
			this.html.el = config.el;
		}
		if(config.forceAnswer) {
			this.config.forceAnswer = config.forceAnswer;
		}
		if(config.forceCorrectAnswer !== undefined)this.forceCorrectAnswer = config.forceCorrectAnswer;
		if(config.labelAnswerButton) {
			this.internal.labelAnswerButton = config.labelAnswerButton;
		}

		this.internal.questions = config.questions;

		if(config.listeners) {
			for(var listener in config.listeners) {
				if(this.validEvents.indexOf(listener)>=0) {
					this.addEvent(listener, config.listeners[listener]);
				}
			}
		}
	},

	_displayQuestion : function() {
		this._clearEl();
		this._addQuestionElement();
		this._addAnsweringOptions();
		this._addAnswerButton();
	},

	_addQuestionElement : function() {
		var el = new Element('div');
		el.addClass('dg-question-label');
		el.set('html', this._getCurrentQuestion().label);
		document.id(this.html.el).adopt(el);
	},

	_addAnsweringOptions : function() {
		var currentQuestion = this._getCurrentQuestion();
		var options = currentQuestion.options;
		var isMulti = currentQuestion.answer.length > 1;

		for(var i=0;i<options.length;i++) {
			var el = new Element('div');
			el.addClass('dg-question-option');

			var option = options[i];
			var id = 'dg-quiz-option-' + this.internal.questionIndex + '-' + i;

			var checkbox = new Element('input', {
				name : 'dg-quiz-options',
				id : id,
				type : isMulti ? 'checkbox' : 'radio',
				value : option
			});

			el.adopt(checkbox);

			var label = new Element('label', { 'for' : id, 'html' : option });
			el.adopt(label);

			document.id(this.html.el).adopt(el);
		}
	},

	_addAnswerButton : function() {
		var el = new Element('div');
		el.addClass('dg-answer-button-container');

		var button = new Element('input');
		button.type = 'button';
		button.set('value', this.internal.labelAnswerButton);
		button.addEvent('click', this._sendAnswer.bind(this));
		el.adopt(button);

		document.id(this.html.el).adopt(el);
	},

	_sendAnswer : function() {
		var answer = this._getAnswersFromForm();

		this.fireEvent('sendanswer', this)
		var currentQuestion = this._getCurrentQuestion();
		if((this.config.forceAnswer || currentQuestion.forceAnswer) && answer.length == 0) {
			this.fireEvent('missinganswer', this);
			return false;
		}

		this.user.answers[this.internal.questionIndex] = answer;

		if(!this._hasAnsweredCorrectly(this.internal.questionIndex) && (this.forceCorrectAnswer || currentQuestion['forceCorrectAnswer'])){
			this.fireEvent('wrongAnswer', this);
			return false;
		}


		this.internal.questionIndex++;

		if (this.internal.questionIndex == this.internal.questions.length) {
			this._clearEl();
			this.fireEvent('finish');
		}
		else {
			this._displayQuestion();
		}
	},

	_getAnswersFromForm : function() {
		var ret = [];
		var els = document.id(this.html.el).getElements('input');
		for(var i=0;i<els.length;i++) {
			if(els[i].checked) {
				ret.push( {
					index : i,
					answer : els[i].value

				});
			}
		}
		return ret;
	},

	_clearEl : function () {
		document.id(this.html.el).set('html','');
	},

	_getCurrentQuestion : function() {
		return this.internal.questions[this.internal.questionIndex];
	},

	start : function() {
		this._displayQuestion();

	},

	getScore : function() {
		var ret = {
			numCorrectAnswers : 0,
			numQuestions : this.internal.questions.length,
			percentageCorrectAnswers : 0,
			incorrectAnswers : []
		};

		var numCorrectAnswers = 0;
		for(var i=0;i<this.internal.questions.length; i++) {
			if(this._hasAnsweredCorrectly(i)) {
				numCorrectAnswers++;
			}else{
				ret.incorrectAnswers.push({
					questionNumber : i+1,
					label : this.internal.questions[i].label,
					correctAnswer : this._getTextualCorrectAnswer(i),
					userAnswer : this._getTextualUserAnswer(i)
				})
			}
		}

		ret.numCorrectAnswers = numCorrectAnswers;
		ret.percentageCorrectAnswers = Math.round(numCorrectAnswers / this.internal.questions.length *100);

		return ret;
	},
	_getTextualCorrectAnswer : function(questionIndex) {
		var ret = [];
		var question = this.internal.questions[questionIndex];
		for(var i=0;i<question.answer.length;i++) {
			var answer = question.answer[i];
			if(question.options.indexOf(answer) == -1) {
				answer = question.options[answer];
			}
			ret.push(answer);
		}
		return ret.join(', ');
	},

	_getTextualUserAnswer : function(questionIndex) {
		var ret = [];
		var userAnswer = this.user.answers[questionIndex];
		for(var i=0;i<userAnswer.length;i++) {
			ret.push(userAnswer[i].answer);
		}
		return ret.join(', ');
	},
	_hasAnsweredCorrectly : function(questionIndex) {
		var correctAnswer = this.internal.questions[questionIndex].answer;
		var answer = this.user.answers[questionIndex];

		if(answer.length == correctAnswer.length ) {
			for(var i=0;i<answer.length;i++) {
				if(correctAnswer.indexOf(answer[i].answer) == -1 &&  correctAnswer.indexOf(answer[i].index) == -1){
					return false;
				}
			}
			return true;
		}

		return false;
	}
});