Switching from one form to another though Script

Hi All,

I have two Contact forms namely "Contractor" & "Agent Contact" and I have a attribute to store the type. When a user open a contact, based on the selected contact type (i.e. Agent/Contractor) I need to switch the form with script. The one I use below worked fine in CRM 2011. However, in CRM 2013 I am getting errors like "Unable to get property 'add_afterSelect' of undefined or null reference", "Unable to get property 'get_isDisposed' of undefined or null refence" & etc... Deployed below code alone (without any other customizations) in a brand new trail edition and got error in that as well...

Code that I used is:-

var FORM_TYPE_CREATE = 1;
var FORM_TYPE_UPDATE = 2;
var AGENT_CONTACT = "1fed44d1-ae68-4a41-bd2b-f13acac4acfa";
var CONTRACTOR = "2ef6278d-1f25-45e4-9da6-7037fe126b63";

function OnFormLoad() {
	formSelector();
}

function formSelector() {
    if (Xrm.Page.ui.getFormType() == FORM_TYPE_CREATE) {
        ContactTypeChanged();
    } else if (Xrm.Page.ui.getFormType() == FORM_TYPE_UPDATE) {
        // Current form name
        var currentFormName = Xrm.Page.ui.formSelector.getCurrentItem().getLabel();

        // Form type
        var type = Xrm.Page.getAttribute("new_contacttype");

        // Disable navigating to different form type
        Xrm.Page.ui.controls.get("new_contacttype").setDisabled(true);

        // logic if type and form name dont match
        if (type.getText() != currentFormName) {
            switch (type.getText()) {
                case "Agent":
                case "Agent Contact":
                    Xrm.Page.ui.formSelector.items.get(AGENT_CONTACT).navigate();
                    break;

                case "Contractor":
                    Xrm.Page.ui.formSelector.items.get(CONTRACTOR).navigate();
                    break;
            }
        }

    }
}

function onChangeType() {
    // Current form name
    var currentFormName = Xrm.Page.ui.formSelector.getCurrentItem().getLabel();

    // Enable Contact Type optionset to set different form type
    Xrm.Page.ui.controls.get("new_contacttype").setDisabled(false);

    // Change form type
    switch (currentFormName) {
        case "Agent Contact":
            Xrm.Page.getAttribute("new_contacttype").setValue("2");
            break;

        case "Contractor":
            Xrm.Page.getAttribute("new_contacttype").setValue("3");
            break;
    }
    // Disable Contact Type optionset
    Xrm.Page.ui.controls.get("new_contacttype").setDisabled(true);
}

If I Change

function OnFormLoad() {
	formSelector();
}

to

function OnFormLoad() {
    setTimeout(function () {
        formSelector();
    }, 1000);
}

it work fine without any errors... With this method there may be possibility of getting same error if the internet connection is slow.

Any suggestions.