Created Unassigned: Missing registry key [135]

I installed the NuGet package, in my Visuals Studio 2013 solution, but when I try to start the R-script engine, I get this exception:

Windows Registry key 'SOFTWARE\R-core' not found in HKEY_LOCAL_MACHINE nor HKEY_CURRENT_USER

Clearly, something went wrong during installation, but what did I miss?

Thanks
Christian