NLua problem

import ('System.Diagnostics')

Process:Start("notepad")

static void Main()
{
    Lua state = new Lua();
    state.LoadCLRPackage();
    string script = File.ReadAllText("script.lua");
    state.DoString(script);
}

Unhandled Exception: NLua.Exceptions.LuaScriptException: [string "chunk"]:3: attempt to index a nil value (global 'Process')
   at NLua.Lua.ThrowExceptionFromError(Int32 oldTop)
   at NLua.Lua.DoString(String chunk, String chunkName)
   at LuaEmbed.Program.Main() in D:\Dev\Sharp\LuaEmbed\LuaEmbed\Program.cs:line 15