sd card / dreamshell difficulties

[Slade]

Dear SWAT team!

First of all I am totally noob in dreamcast modding, so please be patient with me. I downloaded the Dreamshell RC1 + boot loader from this site, burnt the loader onto a disk and put the DS file into the root of the sd card.
When I start the dreamcast with sd plugged in, at the screen where I can select “boot from sd card” I got a massage below: Cant init file system. What does it mean? I tried to format the sd card to Fat32 and ntfs, but got the same massage, and can not go further. Is there any solution for that?

Thanks in advance.