Can't retrieve thumbnails of network based DWG files programmatically

[magg]

Greetings, 

I am one of the developers of the Daminion, the graphic cataloging software that can also manage DWG files and display their previews if a DWG Windows Extension was installed in your Windows.

After installing the DWG TrueView 2015 I was able to see DWG thumbnails in the Windows Explorer, no matter whether they are located in local or network folders.

However I can't retrieve DWG thumbnails programmatically (C#) for DWG files from network folders, but only for DWG files from local folders:

Here is the code fragment written in C#:

using Microsoft.WindowsAPICodePack.Shell;
...
protected Bitmap GetDWGThumbnail(string fileRef)
{
  // this works if fileRef is "C:\DWG\test.dwg" and doesn't work for "\\mediaserver\DWG\test.dwg"
  ShellFile shellFile = ShellFile.FromFilePath(fileRef);
  return shellFile.Thumbnail.LargeBitmap;
}

I'd be appreciated for any input!