I recently installed VS 2013 on a dev computer which uses VS 2010/2012 versions. After successfully building and deploying a new VS 2013 project, I needed to update a prior VS 2012 project. It would not build, needs System.Web.MVC.dll (v. 4.0.20710.0).
The VS2013 replaced System.Web.MVC.dll (v. 4.0.20710.0) with (v. 4.0.40804.0).
I took a VS2012 project backup and copied System.Web.MVC.dll (v. 4.0.20710.0) into the web bin folder and referenced it and set Copy Local to true .
So now the VS2012 project builds and debugs great, just like it used to before installing VS2013.
Now, when I publish the older file is overwritten with the newer System.Web.MVC.dll, which I don't want to use.
Q. Should I add the prior System.Web.MVC.dll (v. 4.0.20710.0) to the GAC?
Q. If so, how do I safely add it and keep both version?
I have never needed to change anything in the GAC before...