>In my case it was a tfs issue, since tfs exclude binaries, so the Nugget PM find the nugget installed and don't update the library If you have similar issue : > •Go to source control > •Navigate to the ..\packages\Microsoft.Web.Optimization >•Add lib folder (uncheck the exclude binary extensions) > •Update your solution and add the dll reference from the path > >NB : the package folder is in the same level of yousolution.sln file >>