Hi, it is likely that Solaris was just not added to the grub configuration.
I would advise trying the following, replacing hd0,0 for the related drive and partition (noting that it starts at drive and partition 0, so if it is the 3rd partition on the 1st hard drive it would be hd0,2. The grub configuration file will likely either be /boot/grub/menu.lst or /boot/grub/grub.conf
title Solaris
rootnoverify (hd0,0)
makeactive
chainloader +1
I found this
here