kernel painic, failed to exec /sbin/modprobe -s -k

[ingirafn@this.is]

"kmod : failed to exec /sbin/modprobe -s -k
VFS : cannot open root device "305" or 03:05

Pleace append a correct "root=" boot option
kernel panic; VFS:unable to mount root fs on 03:05

Hello, this is the message when I try to boot up with my 
compiled 2.4.21 kernel, I did not use initrd, I tried that and does not
matter. I have two other kernels 2.4.18 and 2.4.22 and they both work. 

I cant find out what I did wrong in the compiling prosess.

Anyone?

Ingirafn