When manually building a WP7 solution file on a win64 machine make sure you use the correct version of msbuild.exe - if you don't you'll get the loads of 'failed to load assembly' messages. The message that gives it away is 'Could not load file or assembly PresentationCore': C:\Program Files (x86)\MSBuild\Microsoft\Silverlight for Phone\v4.0\Microsoft.Silverlight.Common.targets(188,9): error MSB4018: S ystem.IO.FileLoadException: Could not load file or assembly 'PresentationCore, Version=3.0.0.0, Culture=neutral, PublicKeyToken=3 1bf3856ad364e35' or one of its dependencies. The given assembly name or codebase was invalid. (Exception from HRESULT: 0x80131047 )\r [C:\Work\Temp\PhoneApp2\PhoneApp2\PhoneApp2.csproj] So get it to build you have to use the msbuild.exe from the standard .net directory - C:\Windows\Microsoft.NET\Framework\v4.0.30319. So the following will fail: And the following will succeed: