Include attribute unknown in .props file - msbuild

Question

I'm preparing a project solution because i plan on publishing a couple nuget projects. In order to avoid the future hassle i've considered to share build properties which are equal in all csproj files.
Oddly enough i get a message saying that the include attribute within the content element is unknown.
Am i doing something wrong/unusual here?
project.v400.csproj
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
<Import Project="..\..\CommonBuildTargets.props"/>
<PropertyGroup>
<Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
<Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
<ProjectGuid>{AA7888A1-E7B4-477F-924E-BF97964B17FA}</ProjectGuid>
<OutputType>Library</OutputType>
<AppDesignerFolder>Properties</AppDesignerFolder>
<RootNamespace>project</RootNamespace>
<AssemblyName>project</AssemblyName>
<TargetFrameworkVersion>v4.0</TargetFrameworkVersion>
<FileAlignment>512</FileAlignment>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
<DebugSymbols>true</DebugSymbols>
<DebugType>full</DebugType>
<Optimize>false</Optimize>
<OutputPath>$(CommonBuildPathDebug)</OutputPath>
<DefineConstants>TRACE;DEBUG;NET400</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
<DebugType>pdbonly</DebugType>
<Optimize>true</Optimize>
<OutputPath>$(CommonBuildPathRelease)</OutputPath>
<DefineConstants>TRACE</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
</PropertyGroup>
<ItemGroup>
<Reference Include="System" />
<Reference Include="System.Core" />
<Reference Include="System.Xml.Linq" />
<Reference Include="System.Data.DataSetExtensions" />
<Reference Include="Microsoft.CSharp" />
<Reference Include="System.Data" />
<Reference Include="System.Xml" />
</ItemGroup>
<ItemGroup>
</ItemGroup>
<Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
<!-- To modify your build process, add your task inside one of the targets below and uncomment it.
Other similar extension points exist, see Microsoft.Common.targets.
<Target Name="BeforeBuild">
</Target>
<Target Name="AfterBuild">
</Target>
-->
</Project>
CommonBuildTargets.props
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<CommonBuildPathDebug>..\Build\$(AssemblyName)\$(Configuration)\$(TargetFrameworkVersion)\</CommonBuildPathDebug>
<CommonBuildPathRelease>..\Build\$(AssemblyName)\$(Configuration)\$(TargetFrameworkVersion)\</CommonBuildPathRelease>
<CommonRecursionRoot>.\src\project.v460\**\*.cs</CommonRecursionRoot>
<CommonContentExclusion>.\src\project.v460\obj\**</CommonContentExclusion>
</PropertyGroup>
<PropertyGroup>
<Content Include="$(CommonRecursionRoot)" Exclude="$(CommonContentExclusion)">
<Link>%(RecursiveDir)%(FileName)%(Extension)</Link>
</Content>
</PropertyGroup>
</Project>
I've tested the the recursive content inclusion individually, which worked fine. Once i extract it to a shared props file (which loads fine too, tested that as well) it does not work anymore.

Answer 1

Well i'd usually delete this question but since i didn't stumble on other questions like this:
The reason it didn't work was because i put my Content element in a propertygroup instead of an itemgroup