can't build default blazor project in 0.5.1

I can't seem to build the default blazor project in 0.5.1 and get the following error:

Error MSB3073 The command "dotnet "C:\Users\R.nuget\packages\microsoft.aspnetcore.blazor.build\0.5.1\targets../tools/Microsoft.AspNetCore.Blazor.Build.dll" write-boot-json obj\Debug\netstandard2.0\WebApplication6.dll --references "C:\Users\R\Source\Repos\WebApplication6\WebApplication6\obj\Debug\netstandard2.0\blazor/bootjson-references.txt" --embedded-resources "C:\Users\R\Source\Repos\WebApplication6\WebApplication6\obj\Debug\netstandard2.0\blazor/embedded.resources.txt" --linker-enabled --output "C:\Users\R\Source\Repos\WebApplication6\WebApplication6\obj\Debug\netstandard2.0\blazor/blazor.boot.json"" exited with code -2147450730. WebApplication6 C:\Users\R.nuget\packages\microsoft.aspnetcore.blazor.build\0.5.1\targets\Blazor.MonoRuntime.targets 635