I created a new ASP.NET MVC 5 web project in VS 2013 (Update 1) then updated all NuGet packages. When I build the project, I get the following warning:
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I updated my package and even reinstalled it - but I was still getting the exact same error as the OP mentioned. I manually edited the referenced dll by doing the following.
I removed the newtonsoft.json.dll from my reference, then manually deleted the .dll from the bin directoy. Then i manually copied the newtonsoft.json.dll from the nuget package folder into the project bin, then added the reference by browsing to the .dll file.
Now my project builds again.