Error building Player: ReflectionTypeLoadException: The classes in the module cannot be loaded.

When attempting to build for Hololens I get the following error:

ReflectionTypeLoadException: The classes in the module cannot be loaded.
System.Reflection.Assembly.GetTypes () (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/Assembly.cs:371)
UnityEditor.AttributeHelper+<CallMethodsWithAttribute>c__Iterator3`1[System.Collections.Generic.IEnumerable`1[UnityEditorInternal.PluginDesc]].MoveNext () (at C:/buildslave/unity/build/Editor/Mono/AttributeHelper.cs:277)
UnityEditor.PluginImporter+<GetExtensionPlugins>c__Iterator0.MoveNext () (at C:/buildslave/unity/build/Editor/Mono/PluginImporter.cs:40)
PostProcessWinRT.CopyPlugins () (at C:/buildslave/unity/build/PlatformDependent/WinRT/SharedSources/CSharp/PostProcessWinRT.cs:401)
PostProcessWinRT.Process () (at C:/buildslave/unity/build/PlatformDependent/WinRT/SharedSources/CSharp/PostProcessWinRT.cs:118)
UnityEditor.Metro.BuildPostprocessor.PostProcess (BuildPostProcessArgs args) (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/ExtensionModule.cs:130)
UnityEditor.PostprocessBuildPlayer.Postprocess (BuildTarget target, System.String installPath, System.String companyName, System.String productName, Int32 width, Int32 height, System.String downloadWebplayerUrl, System.String manualDownloadWebplayerUrl, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.BuildReporting.BuildReport report) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:176)
UnityEditor.HostView:OnGUI()

Any help would be much appreciated because I have no idea what is going on.