apt-get update => boot failure

Hello

I've ubuntu 6.06 sparc server on a sun Ultra 60 box If i do an "apt-get update" and "apt-get upgrade" right know the kernel will be updated.

and after a reboot the silo loading will fail.

I obtain this message

SProgram terminated

Normally at this line it's written Silo ver.. loading ..

i have made a full restore from a .tgz ( i acces the backup and root partition with the restore mode of the cd)

but when i boot again i still have the ``` SProgram terminated

i can only restore my system by making a fresh install and restore the full backup .tgz

so... is there a problem with this update ?
what next ?