title: How to diagnose DataSource.Error when connecting to a custom ADO.NET provider?
body: <p>I have been working on an own implementation of ADO.NET. It works quite well from Visual Studio, etc. but now I want to use it in Power BI Desktop.</p>
  
  <p>I have registered the provider in the machine.config already (both platforms) and have copied all relevant assemblies into the GAC. Now I was finally able to go around the first few error messages Power BI gave me, but now I am stuck at this one:</p>
  
  <blockquote>
    <p>DataSource.Error: An error happened while reading data from the provider: 'Value cannot be null.<br>
    Parameter name: values'<br>
    Details:
    DataSourceKind=AdoDotNet
    DataSourcePath=MyOwnProvider/param1=Something</p>
  </blockquote>
  
  <p>Now it seems to me this is a standard .NET error message, so that would be easy to solve if I knew where it went wrong. Unfortunately I have found no way to diagnose the issue yet. I have tried using Visual Studio to debug Power BI (which seems to have successfully loaded my assembly). I have tried to use DebugView and ProcMon to see what happens, but all failed to give me anything useful.</p>
  
  <p>How to diagnose what actually went wrong? How to get a detailed log, call stack, or whatever?</p>