Personally I dont use Axolotis own file uploader. I think it is much easier putting the SD-card into a computer and just copy/paste the files on to the SD-card, like any usb pen or harddisc.
If you have the option to use a computer for the file transfer try that to start with
BUT.... Remember to format the SD-card with Axolotis formatter first. This is from what I understood really important, that it is formattet with Axolotis formatter and now OSC or windows.