Closed Unassigned: Saving CoffeeScript file produces errors (with Web Essentials) [1599]

I am using Web Essentials extension and whenever I save a CoffeeScript file I get the following error (see below) and the JS preview does not refresh its content.

An exception was thrown when compiling c:\...\test.coffee: System.ArgumentNullException: Value cannot be null.
Parameter name: value
at System.String.StartsWith(String value, StringComparison comparisonType)
at MadsKristensen.EditorExtensions.ProjectHelpers.AddFileToProject(String parentFileName, String fileName)
at MadsKristensen.EditorExtensions.NodeExecutorBase.<ProcessResult>d__9.MoveNext()

This behavior takes place only in Node.js projects. Not sure whether this is caused by Web Essentials or Node.js Tools, so I am posting it here too.

Configuration: VS Express 2013 for Web Update 4, NTVS 1.0 RC VS 2013, Web Essentials 2013.