Problem: Unable to resolve dependencies of NuGet packages

When you upgrade the site by installing Telerik.Sitefinity.All NuGet package, Visual Studio throws the following error:

Unable to resolve dependencies. 'Progress.Sitefinity.Authentication 10.0.6421' is not compatible with 'Telerik.Sitefinity.Core 10.1.6523
Unable to resolve dependency 'Telerik.Sitefinity.AmazonCloudSearch'. Source(s) used: 'Sitefinity NuGet Server', 'nuget.org', 'Microsoft Visual Studio Offline Packages.

The cause for this error is that NuGet cache conflicts with the build of the site. 

To resolve the problem, perform the following:

1. Clear the NuGet cache files.
   You do this in the following way:
   1. In the toolbar of Visual Studio, navigate to Tools » NuGet Package Manager » Package Manager Settings.
      
   2. In the left pane, navigate to NuGet Package Manager » General.
      
   3. Click Clear All NuGet Cache(s).
      
2. Confirm that the Sitefinity NuGet Server (http://nuget.sitefinity.com/nuget) is configured in Visual Studio.
   To do this, navigate to Tools » NuGet Package Manager » Package Manager Settings » Package Sources.
3. Delete all packages from the packages folder, located in your project's folder.
   
4. Reinstall Telerik.Sitefinity.All to the desired version.
5. Rebuild the project.