When you start using NuGet you’ll notice that the packages.config file it creates is part of your project but the packages directory isn’t part of the solution. If you’re using version control the chances are that your packages directory isn’t being committed to that either (this is actually a good thing).
So how do you install packages listed in the packages.config? While there’s currently no way to do it from inside Visual Studio you can do it from the command line. Start by downloading the NuGet.exe Command Line. Once you have that open a command prompt and change to the solution directory. Now run the following command for each project folder.
c:\path\to\nuget.exe install -o packages project-folder\packages.config
This will download the required packages and put them into the packages folder where the NuGet package manager would have installed them originally. Visual Studio should now find any missing assemblies. The NuGet command line installer is smart enough to only download packages that it doesn’t already have so if two projects in your solution require the same package it will only be downloaded once.