Adding an OOTB Web Part to an App for SharePoint

Question

I'm attempting to just add an OOTB Web Part (actually to create a variation of a Search Page) in an App for SharePoint using an Office 365 Development Site for development but this happens with ANY OOTB Web Part. The default code when I create a page of course is this:

<%@ Page language="C#" MasterPageFile="~masterurl/default.master"
    Inherits="Microsoft.SharePoint.WebPartPages.WebPartPage, 
    Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, 
    PublicKeyToken=71e9bce111e9429c" %>
<%@ Register Tagprefix="Utilities" Namespace="Microsoft.SharePoint.Utilities" 
    Assembly="Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, 
    PublicKeyToken=71e9bce111e9429c" %>
<%@ Register Tagprefix="WebPartPages" Namespace="Microsoft.SharePoint.WebPartPages" 
    Assembly="Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral,
    PublicKeyToken=71e9bce111e9429c" %>
<%@ Register Tagprefix="SharePoint" Namespace="Microsoft.SharePoint.WebControls"
    Assembly="Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, 
    PublicKeyToken=71e9bce111e9429c" %>

<asp:Content ContentPlaceHolderId="PlaceHolderAdditionalPageHead" runat="server">
  <SharePoint:ScriptLink name="sp.js" runat="server" OnDemand="true" 
      LoadAfterUI="true" Localizable="false" />
</asp:Content>

<asp:Content ContentPlaceHolderId="PlaceHolderMain" runat="server">
  <WebPartPages:WebPartZone runat="server" FrameType="TitleBarOnly" 
      ID="full" Title="loc:full" />
</asp:Content>

And I just want to add, say, the SearchArea Web Part into the Zone I always get this on testing: "Cannot create XmlSerializers for this Web Part"

This seems so simple and yet I always get this error. This essentially happens with ANY OOTB Web Part. What am I doing wrong? Again, I just have an App for SharePoint that will deploy a heavily customized Search experience, but MUST use the OOTB SharePoint controls for Search in certain areas.

Thoughts?