I found a way to write files on my USB 500Gb disk: First I use EsExplorer pro (haven't test with free). Reset EsExplorer then you will have two entry for disk in local file, a numerical (SD) and USBxxxx, choose numerical one and when you will try to write a file or folder a popup message will ask you to add place. If you do not see your disk in upper right choose show sdcard and add root of your disk. Never add USBxxxx because doing so you will loose access to disk, always use numerical entry. Edit: I test with EsExplorer free. Use external storage in replacement of numerical, do not use USB and it will work.
