Invalid argument jquery-1.6.2 line 8538

HTML

<input type="password" value="" name="password" id="register_password">
        <ul class="well-bad invisible" id="pass_strength_container" style="display: block;">
            <li id="password_strength">
                <div class="passwordStrengthBar" style="width: 100px;"><div style=" overflow: hidden;" class="strong"></div></div>
            </li>
            <li class="password_text" id="password_text">Strong</li>
        </ul>

CSS

.passwordStrengthBar {
    background: white;
    border: 1px solid #777777;
    width: 100px;
}

.passwordStrengthBar div {
    height: 5px;
    width: 0%;
}

.passwordStrengthBar div.strong {
    background-color: #32cd32;
}

.passwordStrengthBar div.medium {
    background-color: yellow;
}

.passwordStrengthBar div.weak {
    background-color: orange;
}

.passwordStrengthBar div.useless {
    background-color: red;
}

JavaScript

/* Intelligent Web NameSpace */
var IW = IW || {};

/** 
 * Password validator logic
 */ 
(function(IW) {
    
    var secondsInADay = 86400;
    
    function PasswordValidator() {
    }
    
    /**
     * How long a password can be expected to last
     */
    PasswordValidator.prototype.passwordLifeTimeInDays = 365;
    
    /**
     * An estimate of how many attempts could be made per second to guess a password
     */
    PasswordValidator.prototype.passwordAttemptsPerSecond = 500;
     
    /**
     * An array of regular expressions to match against the password. Each is associated
     * with the number of unique characters that each expression can match.
     * @param password
     */
    PasswordValidator.prototype.expressions = [
        {
            regex : /[A-Z]+/,
            uniqueChars : 26
        },
        {
            regex : /[a-z]+/,
            uniqueChars : 26
        },
        {
            regex : /[0-9]+/,
            uniqueChars : 10
        },
        {
            regex : /[!\?.;,\\@$£#*()%~<>{}\[\]]+/,
            uniqueChars : 17
        }
    ];
    /**
     * Checks the supplied password
     * @param {String} password
     * @return The predicted lifetime of the password, as a percentage of the defined password lifetime.
     */
    PasswordValidator.prototype.checkPassword = function(password) {
     
        var
                expressions = this.expressions,
                i,
                l = expressions.length,
                expression,
                possibilitiesPerLetterInPassword = 0;
           
        for (i = 0; i < l; i++) {
           
            expression = expressions[i];
           
            if (expression.regex.exec(password)) {
                possibilitiesPerLetterInPassword += expression.uniqueChars;
            }
           
        }
           
        var
                totalCombinations = Math.pow(possibilitiesPerLetterInPassword, password.length),
            // how long, on average,...