Help modifying WPF main window template - namespace error

I am a complete Blend novice with 2 day’s experience so please forgive me if my terminology makes no sense. I’m using Blend 3 Mix09 Preview, and I’m trying to modify the main window template of a WPF UI so that I can change the main window borders, title bar & control buttons. I go through the process of creating a ControlTemplate resource and modify the properties of the window parts I want to change. I then attempt to build the project and I get the following error:

“The type or namespace name ‘Expression’ does not exist in the namespace ‘Microsoft’ (are you missing an assembly reference?)” in file MainWindow.g.cs

Here are the steps I take:

[]New project: “Test1”; right-click on the top-level Window object in the Objects & Timeline area.Select > Edit Control Parts (Template) > Edit a Copy
]In the Create ControlTemplate Resource dialog I give it the name MyTemplate and select Define in This document (with Window:Window selected).

[]In Objects & Timeline I now see the scope change to MyTemplate (WindowInstance Template) with the Template object and its constituent parts:

]I select the 'topResizeFrame" object which then displays all the options in Properties panel. I change a couple of things such as color and width. I repeat this for the left, right and bottom ResizeFrames, and make some similar changes to the caption object.
[]Returning to the main window, I see the original window and what looks like an inset of the template I just created with frame colors and size as I specified.

]I build the project and get the namespace error mentioned above.

I’ve read this excellent tutorial on custom WPF windows, but was hoping to take the seemingly easier route of modifying an existing window template so as to maintain the system functions such as min/maximize, border resize and window drag (C# coding isn’t my strongest point).

Any suggestions would be very much appreciated.