unable to boot on the netinst CD

[Pooly <pooly7@gmail.com>]

Hi all,

I'm trying to install a Debian 3.1 on an Ultra5. When I boot on the CD
(3.1r0a-sparc-netinst) I end up with a kernel panic with :
Ramdisk : couldn't find valid RAM disk image starting at 0
Cramfs: wrong magic

I've google a bit, and I've found nothing which works. 
Any hints on this ?
thanks,