Error running XUnit tests in VS2013 / ReSharper 8 - xunit.dll not found

I've upgraded all the xUnit NuGet packages in my solution to XUnit 2.1 in the hope of fixing some problems I had running my xUnit tests, but I'm getting the same problem as before, which is:

[Window Title] Unit Test Runner

[Main Instruction] Unit Test Runner failed to run tests

[Content] System.ArgumentException: Could not find file: C:\Users\myuser\mysolution\myproject\bin\Debug\ xunit.dll

[Expanded Information] at Xunit.ExecutorWrapper..ctor(String assemblyFilename, String configFilename, Boolean shadowCopy) at XunitContrib.Runner.ReSharper.RemoteRunner.TestRunner.Run(XunitTestAssemblyTask assemblyTask, TaskProvider taskProvider) at XunitContrib.Runner.ReSharper.RemoteRunner.XunitTaskRunner.ExecuteRecursive(TaskExecutionNode node) at JetBrains.ReSharper.TaskRunnerFramework.StartupTaskRunnerHost.Execute(TaskExecutionNode node)

I've tried un-installing, re-installing, cleaning and rebuilding, etc. etc. for hours and got nowhere.

I'm using Visual Studio 2013 update 5, ReSharper 8.2.1, and have installed the following NuGet packages:

<package id="xunit" version="2.1.0" targetFramework="net451" />
<package id="xunit.abstractions" version="2.0.0" targetFramework="net451" />
<package id="xunit.assert" version="2.1.0" targetFramework="net451" />
<package id="xunit.core" version="2.1.0" targetFramework="net451" />
<package id="xunit.extensibility.core" version="2.1.0" targetFramework="net451" />
<package id="xunit.extensibility.execution" version="2.1.0" targetFramework="net451" />
<package id="xunit.MSBuild" version="2.0.0.0" targetFramework="net451" developmentDependency="true" />
<package id="xunit.runner.msbuild" version="2.1.0" targetFramework="net451" />
<package id="xunit.runner.visualstudio" version="2.1.0" targetFramework="net451" />

To be fair, there is no file called xunit.dll in the bin folder, but... I've installed everything I can find, and I'm at a loss as to what else I can do.

Suggestions very welcome.