ItemGroup 'Folder' missing

[dnperfors]

Given the following project file, I get a "The given key was not present in the dictionary." exception when I ask for the Contents of an ItemGroup:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <ProjectGuid>{E90B1572-820F-4581-9351-DB36703E6846}</ProjectGuid>
    <AppDesignerFolder>Properties</AppDesignerFolder>
    <RootNamespace>Test</RootNamespace>
    <AssemblyName>Test</AssemblyName>
  </PropertyGroup>
  <ItemGroup>
    <Folder Include="Properties\" />
  </ItemGroup>
  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
</Project>

[dnperfors]

Actually, that is not the correct exception I get... The exception was that the constructor of ItemGroupContent couldn't be found...