You have projects relying on NuGet packages. Some of these NuGet packages have been updated and you know this. However, for one reason or another, perhaps the NuGet packages do not increment their version for each new release, Visual Studio does not observe the packages have changed and, therefore does not update them. What do you do?
Quick and dirty solution is to just delete these respective NuGet packages from these two places and then build your solution again.
- Local NuGet repository: on my Windows 8 machine it is found here: C:\Users\my-username\.nuget\packages
- Local NuGet cache for the packages in this solution. This folder is typically found in the root of the solution.
Do this and you are good to go.