Can't change the master page after upgrading to SharePoint 2013.

Question

After upgrading our farm to SharePoint 2013 we are having trouble changing the master page for sites that don't have sub-sites. We are still using the v4 UI version, and that appears to be what is causing the problem. The error we get when going to /_layouts/ChangeSiteMasterPage.aspx
is:
System.NullReferenceException: Object reference not set to an instance of an object.    at Microsoft.SharePoint.Publishing.Internal.CodeBehind.AreaChromeSettingsPage.OnLoad(EventArgs e)     at System.Web.UI.Control.LoadRecursive()    
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
I took a peek at the source code for AreaChromeSettingsPage.OnLoad and found that it references a CheckBox control that does not exist in the v4 ChangeSiteMasterPage.aspx:
protected override void OnLoad(EventArgs e)
base.OnLoad(e);
this.EnsureChildControls();
if (!this.Page.IsPostBack)
this.LoadValues();
if (base.Web.Webs.Count == 0)
this.resetSystemMasterPageSubSitesCheckBox.Visible = false;
this.resetSubSitesCheckBox.Visible = false;
this.resetAlternateCssSubSitesCheckBox.Visible = false;
this.resetThemeSubSitesCheckBox.Visible = false;
base.ConfigureCancelButton(this.BtnCancel);
If I manually add a checkbox control with the ID "resetThemeSubSitesCheckBox" to a hidden panel in the v4 copy of ChangeSiteMasterPage.aspx the page works, but obviously this is not a best practice. How can we fix this without upgrading the UI version, which
we are not yet ready to do?

Answer 1

Thanks Mike - Could you please share what is your next step then? I also have custom master pages and layout but I am going to make new master page and layout in 2013 as we need to change the existing branding too. so, i upgrade the site collection. I understand
the Look and Feel will not persist after the upgrade but I am concern that at least the page should show the content on the page after the upgrade. The page had Calendar webppart on it but after the upgrade it is coming blank.
any suggestion?
Regards,
Khushi
Khushi