@bigbarthy,
I would definitely first take a look at the USB sharing accounts and make sure that you have both read and write access for the share/ account you are logging in with
Have you tried transferring a file from another device? It could be possible that either you have not enabled SMB in your network adapter settings, or you have a security setting, such as private v public network, that is preventing the transfer from taking place.
I would recommend taking a look at this FAQ for File Sharing on USB Drives for any settings or options that are different