Could not load file or assembly 'System.Windows.Interactivity' [duplicate]

Just a guess, might be you are not referencing the libraries in the MAIN project.

It has happened to me several times.

Tilak's answer helped me out a big deal, but I also needed to name at least one element from assembly "i" in the XAML code.When the element is named, Visual Studio correctly hooks up the assembly.

Change

<i:InvokeCommandAction Command="{Binding MyCommand}"/>

into

<i:InvokeCommandAction Command="{Binding MyCommand}" x:Name="interactivityFix" />

This needs to be done to only one element in the entire XAML file.

Sometimes, when you add a new library, in introduces a clashing version of System.Windows.Interactivity.dll.

This prevents the project from working.

To fix, add an Assembly Binding Redirect by editing your app.config to look something like this:

<?xml version="1.0"?><configuration><runtime>  <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">    <dependentAssembly>      <assemblyIdentity name="System.Windows.Interactivity"                        publicKeyToken="31bf3856ad364e35"                        culture="neutral"/>      <bindingRedirect oldVersion="4.0.0.0"                       newVersion="4.5.0.0" />    </dependentAssembly>  </assemblyBinding></runtime><startup><supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5"/></startup><appSettings>  <add key="TestKey" value="true"/></appSettings>

Don't worry about changing the PublicKeyToken, that's constant across all versions, as it depends on the name of the .dll, not the version.

Ensure that you match the newVersion in your appConfig to the actual version that you end up pointing at: