The WSUS content directory is not accessible.

2012R2 moved content to a QNAP NAS. NTFS Permissions I believe are correct
Error:-
System.UnauthorizedAccessException: Access to the path '\\x.x.x.x\wsuscontent\WsusContent\anonymousCheckFile.txt' is denied.

I can open and edit the file using the link on the event log - any ideas please ?