The latest version from the forwarder channel is 5.1 from 2012/13. So i will think he is using it.
USB Sticks have very bad compatibility for use with USB Loader GX. If you formated it with guiformat to fat32 with 32kb sectorsize and checked it already with Powershell for errors with chkdsk X: /r. You might try wbfs filesystem on it, but it only supports Wii games.