System.InvalidOperationException: Could not resolve mscorlib for target framework '.NETStandard,Version=v1.0'

Repro:

Can't repro this again. Did something like:

- Create a new .NET Core xUnit test proj
- Add another .NET Core class lib proj to the solution
- Change the target framework for the class lib proj from ```netcoreapp1.0``` to ```netstandard1.0``` as save.

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1/23/2017 4:49:52 PM
Crippling
System.AggregateException: One or more errors occurred. ---> System.InvalidOperationException: Could not resolve mscorlib for target framework '.NETStandard,Version=v1.0'. This can happen if the target framework is not installed or if the framework moniker is incorrectly formatted.
at Microsoft.VisualStudio.Shell.Design.VsTargetFrameworkUniverse..ctor(IDesignTimeAssemblyLoader assemblyLoader, IVsDesignTimeAssemblyResolution projectAssemblyResolution, IVsSmartOpenScope dispenser)
at Microsoft.VisualStudio.Shell.Design.VsTargetFrameworkUniverse.GetUniverse(IDesignTimeAssemblyLoader assemblyLoader, IVsDesignTimeAssemblyResolution projectAssemblyResolution, IVsSmartOpenScope dispenser)
at Microsoft.VisualStudio.Shell.Design.VsTargetFrameworkProvider..ctor(IVsDesignTimeAssemblyResolution assemblyResolution, IDesignTimeAssemblyLoader assemblyLoader, TypeDescriptionProvider parentProvider, IVsSmartOpenScope openScope)
at Microsoft.VisualStudio.ProjectUtilities.GetTargetFrameworkProvider(IServiceProvider provider, IDesignTimeAssemblyLoader assemblyLoader, IVsHierarchy hierarchy, Object instance)
at Microsoft.VisualStudio.Design.VSTypeResolutionService.get_TypeProvider()
at Microsoft.VisualStudio.Design.VSTypeResolutionService.ClearReferenceEntries(Boolean normal, Boolean project, Boolean disposing)
at Microsoft.VisualStudio.Design.VSTypeResolutionService.VSLangProj._dispReferencesEvents.ReferenceRemoved(Reference r)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.Package.Automation.OAVSReferences.OnReferenceRemoved(Reference reference)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.Package.ReferencesHostBridge.ApplyAsync(ReferencesDelta value)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.Package.ProjectHostBridge`3.<>c__DisplayClass36_1.<b__3>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.JoinableTask.d__76.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.JoinableTask`1.d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.Package.ProjectHostBridge`3.<>c__DisplayClass36_0.<b__2>d.MoveNext()
--- End of inner exception stack trace ---
---> (Inner Exception #0) System.InvalidOperationException: Could not resolve mscorlib for target framework '.NETStandard,Version=v1.0'. This can happen if the target framework is not installed or if the framework moniker is incorrectly formatted.
at Microsoft.VisualStudio.Shell.Design.VsTargetFrameworkUniverse..ctor(IDesignTimeAssemblyLoader assemblyLoader, IVsDesignTimeAssemblyResolution projectAssemblyResolution, IVsSmartOpenScope dispenser)
at Microsoft.VisualStudio.Shell.Design.VsTargetFrameworkUniverse.GetUniverse(IDesignTimeAssemblyLoader assemblyLoader, IVsDesignTimeAssemblyResolution projectAssemblyResolution, IVsSmartOpenScope dispenser)
at Microsoft.VisualStudio.Shell.Design.VsTargetFrameworkProvider..ctor(IVsDesignTimeAssemblyResolution assemblyResolution, IDesignTimeAssemblyLoader assemblyLoader, TypeDescriptionProvider parentProvider, IVsSmartOpenScope openScope)
at Microsoft.VisualStudio.ProjectUtilities.GetTargetFrameworkProvider(IServiceProvider provider, IDesignTimeAssemblyLoader assemblyLoader, IVsHierarchy hierarchy, Object instance)
at Microsoft.VisualStudio.Design.VSTypeResolutionService.get_TypeProvider()
at Microsoft.VisualStudio.Design.VSTypeResolutionService.ClearReferenceEntries(Boolean normal, Boolean project, Boolean disposing)
at Microsoft.VisualStudio.Design.VSTypeResolutionService.VSLangProj._dispReferencesEvents.ReferenceRemoved(Reference r)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.Package.Automation.OAVSReferences.OnReferenceRemoved(Reference reference)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.Package.ReferencesHostBridge.ApplyAsync(ReferencesDelta value)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.Package.ProjectHostBridge`3.<>c__DisplayClass36_1.<b__3>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.JoinableTask.d__76.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.JoinableTask`1.d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.Package.ProjectHostBridge`3.<>c__DisplayClass36_0.<b__2>d.MoveNext()<---

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```