kernel panic: no init found with 2.5.32

[Stefano Biella]

I have a slackware 8.1 machine that works fine with 2.4.18/19 kernels,
but,when I reboot with the 2.5.31/32 kernels, the system have a "kernel
panic: no init found. try passing init= option to kernel" The fs is a
reisersfs v.3.6 on Intel PIIX4 chipset with udma33 disk.
The disk is not corrupted because if I back to 2.4.X the machine boot
fine.

what's wrong?