At the moment, if the directory "AutoGeneratedSource" isn't already there, the dotNetInterfaceGenerator dies. There are legitimate reasons why the directory wouldn't be there: If the project is under source control, AutoGeneratedSource may not be included in the source control because it's auto generated. If this directory isn't present, it should be created.
Add extra line to file xlwDotNet\DotNetInterfaceGenerator\Program.cs
Line 76: IO.Directory.CreateDirectory(dirName);