We are sorry for the late reply.
This error may indicate a temporary connectivity issue. Could you please give it another try? If that is not the case let us know:
1. The version of NuGet Package Manager.
2. The version of Microsoft .NET Core Tools.
3. Which update is installed in your Visual Studio 2015.
4. Does this error occurs with other Telerik packages?
The versions we ask for could be found in the About Microsoft Visual Studio dialog (Help | About Microsoft Visual Studio).
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