The module expects the file to be in the resource directory of your implementation and not as a file document, as far as I can tell from the forum post you mentioned.
The error shows that it is trying to retrieve a file from the C-drive in the resources directory and not from the filedocument that you have uploaded. Not sure if this is possible with the module.
Importing the file from the filedocument is possible with the following module: https://appstore.home.mendix.com/link/app/429/Erwin-'t-Hoen/Flat-&-delimited-file-import