Using SqlClient can cause a DllNotFoundException on sni.dll. This has been reported a few times by customers trying to use SqlClient on coreclr-x64/x86 on Windows (see dotnet/aspnetcore#904 for detailed symptoms). One of the possible causes is that you may need the Microsoft Visual C++ 2012 Redistributable installed to get SqlClient to work.

Beta8 has not solved the problem, e.g. link /dump /imports sni.dll still shows MSVCR110.dll in the list of dependencies.

From an email thread with @ericstj it seems that it should use msvcrt.dll instead.