Unable to get property 'length' of undefined or null reference on CRM 2011 form on IE11

I have and onchange function set up on a field on my Lead CRM 2011 form. Everything works correctly on IE9, but after upgrading to IE11 I get an onchange event error. 

Unable to get property 'length' of undefined or null reference

Here is my code:

function leadsourcecode_onchange() {
    //LeadSourceCode OnChange --winner
    //"Right" function
    function Right(str, n) {
        if (n <= 0)
            return "";
        else if (n > String(str).length)
            return str;
        else {
            var iLen = String(str).length;
            return String(str).substring(iLen, iLen - n);
        }
    }

    var oLeadsourcecode = crmForm.all.leadsourcecode;
    var oSecondaryLeadsourcecode = crmForm.all.new_secondaryleadsource;
    var oFilter = null;
    var currentselectedvalue = oSecondaryLeadsourcecode.DataValue;

    oSecondaryLeadsourcecode.Disabled = false;


    // Get Sub-Category Filter
    oFilter = Right(oLeadsourcecode.SelectedText, 2);



    var iIndex = 0;
    var text1 = null;

    // Set the picklist back to the original value
    oSecondaryLeadsourcecode.Options = oSecondaryLeadsourcecode.originalPicklistOptions;

    // Create a new array, which will hold the new picklist options
    var oTempArray = new Array();

    // Initialize the index for the temp array
    var iIndex = 0;
    var iNewIndex = 0;


    for (var i = 0; i < oSecondaryLeadsourcecode.originalPicklistOptions.length; i++) {

        oSecondaryLeadsourcecode.DataValue = i;
        text1 = oSecondaryLeadsourcecode.children[i].innerHTML;

        if (i == 0) {
            oSecondaryLeadsourcecode.DataValue = 0;

            // Found the required field
            oSecondaryLeadsourcecode.AddOption(text1, 0);
            iNewIndex = oSecondaryLeadsourcecode.selectedIndex;
            oTempArray[iIndex] = oSecondaryLeadsourcecode.originalPicklistOptions[0];
            iIndex++;
        }

        // Search for filter in text1    
        if (text1.indexOf(oFilter) != -1) {
            oSecondaryLeadsourcecode.DataValue = i;

            // Found the required field
            oSecondaryLeadsourcecode.AddOption(text1, i);
            iNewIndex = oSecondaryLeadsourcecode.children[i].index;
            oTempArray[iIndex] = oSecondaryLeadsourcecode.originalPicklistOptions[iNewIndex];
            iIndex++;

        }
    }
    // Reset the Sub-Industry picklist with the new options
    oSecondaryLeadsourcecode.Options = oTempArray;
}

When I turn on debugging in IE11 it shows a DOM7011 error. "The code on this page disabled back and forward caching. For more information, see: go.microsoft.com/fwlink"

Thanks for any assistance,

-Brian