How to use the MSBuild Task?

Jul 29, 2014 at 3:04 PM
The documentation seems to indicate that there is a build task for WebGrease, which I'd like to take advantage of. However, when I add the task to my project as described in the documentation, it does not work. Here's how I added the task to my .csproj file:
  <UsingTask TaskName="WebGreaseTask" AssemblyName="WebGrease, Version=1.6.5135.21930, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL" />
  <Target Name="MinifyCss" AfterTargets="DotLessBuildTasksDotNet">
    <WebGreaseTask />
When I try to build my project, I get the following error:
The "WebGreaseTask" task could not be loaded from the assembly WebGrease, Version=1.6.5135.21930, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL. Could not load file or assembly 'WebGrease, Version=1.6.5135.21930, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.
WebGrease was added to my project via the NuGet package, and I can see it is registered in the project file, and there's even a version redirect in my project.

Are there steps or attributes I'm missing in the config?