It sounds like you are trying to add the Tobii.EyeX.Client.dll as a managed dll. You cannot do that, since it is a native dll. I know how to add it in a C# project and I’m guessing it should be similar in VB.NET (though I have never tried).
Check out this forum topic and the solution I proposed there:
If that doesn’t work, I suggest you google “reference native dll vb.net”.