GSR Collector failing - Error 28 (SM 5.1)

I'm trying to get the GSR Collector working on a new installation of Storage Manager 5.1. I've been tackling various issues which are mostly related to bad data (long paths, dodgy NTFS permissions etc). This one is perplexing me though as I can't see anything specifically wrong with the folder that GSR is failing on.

The logs are giving "result = 163" which I believe is an issue with unknown characters. GSR fails with "Scan Failed: File System Path could not be found. (28)".