TFS 2010 build failing because it can't load M

My TFS 2010 builds are failing inexplicably. The unit tests are passing, there are no warnings or errors. The build runs completely, beginning to end, but is partially succeeding. It took a while for me to find any error at all--I had to download the test results and then click a link at the top labelled "Test run error". The error is:

Error   01/14/2013 1:31:47 AM   The diagnostic data adapter 'Microsoft.VisualStudio.TestTools.CodeCoverage.CoveragePlugIn, Microsoft.VisualStudio.QualityTools.Plugins.CodeCoverage, Version=11.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' on agent 'BuildServer3' threw an exception during type loading, construction, or initialization: System.IO.FileLoadException: Could not load file or assembly 'Microsoft.VisualStudio.QualityTools.Plugins.CodeCoverage, Version=11.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
File name: 'Microsoft.VisualStudio.QualityTools.Plugins.CodeCoverage, Version=11.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
   at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMarkHandle stackMark, Boolean loadTypeFromPartialName, ObjectHandleOnStack type)
   at System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark, Boolean loadTypeFromPartialName)
   at System.RuntimeType.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark)
   at System.Type.GetType(String typeName, Boolean throwOnError)
   at Microsoft.VisualStudio.TestTools.DataCollection.ExecutionPluginManager.LoadAndInitDataCollectorAsync(TestRun testRun, String collectorTypeName, Dictionary`2 dataCollectorCache)

This is from a Visual Studio 2012 solution, the build server runs Visual Studio 2010...so I'm guessing that's why it's failing.

I figured out the problem.

I had created a CodeCoverage.testsettings file to measure Code Coverage during the builds...but I created the file in Visual Studio 2012. I found this entry in the file using my favorite text editor:

<DataCollector uri="datacollector://microsoft/CodeCoverage/1.0" assemblyQualifiedName="Microsoft.VisualStudio.TestTools.CodeCoverage.CoveragePlugIn, Microsoft.VisualStudio.QualityTools.Plugins.CodeCoverage, Version=11.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" friendlyName="Code Coverage (Visual Studio 2010)">

I saw a Version of 11.0.0.0 in there (which must have been generated by Visual Studio 2012). I just changed it to 10.0.0.0 using my text editor:

<DataCollector uri="datacollector://microsoft/CodeCoverage/1.0" assemblyQualifiedName="Microsoft.VisualStudio.TestTools.CodeCoverage.CoveragePlugIn, Microsoft.VisualStudio.QualityTools.Plugins.CodeCoverage, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" friendlyName="Code Coverage (Visual Studio 2010)">

The build now works as expected.