Post #6, the NtDirect.dll is a managed dll and must be P/invoke imported into your project. You will not be able to add this to the references.
Below is a link to an example of Platform Invoke on a dll.
https://msdn.microsoft.com/en-us/library/55d3thsc.aspx
For example:
[System.Runtime.InteropServices.DllImport("C:\\Windows\\SysWOW64\\NtDirect.dll")] public static extern int Connected(int showMessage);
Alternatively, the NinjaTrader.Client.dll is not managed and can be directly added to the references in your project.
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