JavaScript runtime error: Unable to get property 'createRange' of undefined or null reference

I am trying to use below code in keypress 

http://jsfiddle.net/S9G8C/203/

But i am getting error : 0x800a138f - JavaScript runtime error: Unable to get property 'createRange' of undefined or null reference.

i know i passing wrong value here,please help me.

var caratPos = getSelectionStart(this);

I am using like

        $("[id*=txtPrice]").keypress(function (e) {
            if (e.which != 8 && e.which != 0 && (e.which < 48 || e.which > 57) && (e.which != 46)) {
                return false;
            }
            var charCode = (e.which) ? e.which : e.keyCode;
            var number = this.value.split('.');
              //just one dot
            if (number.length > 1 && charCode == 46) {
                return false;
            }
            //get the carat position
            var caratPos = getSelectionStart(this);
            alert(this.value + ' and  ' + caratPos);
            var dotPos = this.value.indexOf(".");
            if (caratPos > dotPos && dotPos > -1 && (number[1].length > 1)) {
                return false;
            }
            return true;

        });

        function getSelectionStart(o) {
            if (o.createTextRange) {
                var r = document.selection.createRange().duplicate()
                r.moveEnd('character', o.value.length)
                if (r.text == '') return o.value.length
                return o.value.lastIndexOf(r.text)
            } else return o.selectionStart
        }