Tim,
There's a couple things you can check:
- Make sure the file isn't read-only.
- Make sure the user assigned to the service has proper Read and Write permissions to this folder.
First two things to check. If it still doesn't pick it up, it may be that the service is currently processing the previous file that you've sent, and hasn't finished processing it, so you may have to wait. (or kill the service, flush the temporary files and restart it if you think that it's stuck)
I would start with that. Let us know how it goes!
Regards,
Raphaël Lalonde Lefebvre