问题
I've got a project that targets .Net 4.0, and one of the referenced assemblies is .Net 4.5.
Until I installed .Net 4.5 this was working fine, however after the install I get five warnings regarding the targeted .Net version along these lines:
*The primary reference "xxxx.Library, Version=1.0.0.1, Culture=neutral, processorArchitecture=MSIL" could not be resolved because it was built against the ".NETFramework,Version=v4.5" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.0"
And this:
The primary reference "Microsoft.TeamFoundation.Build.Workflow, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the framework assembly "System.IO.Compression, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" which could not be resolved in the currently targeted framework. ".NETFramework,Version=v4.0". To resolve this problem, either remove the reference "Microsoft.TeamFoundation.Build.Workflow, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" or retarget your application to a framework version which contains "System.IO.Compression, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089". Tests
Why does Visual Studio hate me? If it could compile before the update to 4.5, the targeted framework has not changed and it still works for a colleague on VS2010 with .Net 4 why am I being stuffed?
回答1:
The error message explains the problem - a .NET 4 app can't reference a .NET 4.5 dll. Change your app to .NET 4.5 as well, or change the dll back to .NET 4.
回答2:
It's because for reasons best known to Microsoft, the .NET Framework 4.5 is an in-place update that replaces your .NET Framework 4 files (rather than a side-by-side installation). If you look in C:\Windows\Microsoft.NET, you won't find a 4.5 folder--it replaced the files in your 4.0 folder.
So the reason it compiled before is that the dll was a .Net 4.0 dll then. Now it's been replaced by a 4.5 one.
来源：https://stackoverflow.com/questions/16856474/upgrade-to-net-4-5-causes-assembly-to-fail