Put some Debug.Prints in the code then and ask the user to go to the debug screen and send you what is displayed by copy and paste.
Alternatively if you can remote to his machine, do the work yourself.
Have you checked what that user's userprofile is?
Always hard to see what might be the cause when people change things, even if it is to redact a name
Are you able to logon as them and run the code?
looking back,
@Pat Hartman had a good question, how can you use the C: drive, which is generally the local PC.?
Can you show your drives within Explorer or does that have to be redacted as well?
Edit: Perhaps show the results of the set command for you and the other user.?
Leave at least the start of the path alone if you are going to redact the rest of the path.