What are you putting in to the source parameter of the FilenamePartExtractor?

There's two internal attributes that may be useful, you can expose these on the reader under the "Format Attributes" tab. They're fme_basename, which contains the filename (e.g. if you selected roads.shp fme_basename would hold the value roads) and fme_dataset, which contains the full path. If you put in fme_dataset as the input for the FilenamePartExtractor it will split that into its component parts (but if fme_basename already has what you want you don't need the FPE)