Starting with the Solaris 10 8/07 release, for SPARC systems, you can upgrade the Solaris OS only from the following releases:
Solaris 8 OS
Solaris 9 OS
Solaris 10 OS
For x86 systems, you can upgrade the Solaris OS only from the following releases:
Solaris 9 OS
Solaris 10 OS
To upgrade releases previous to the Solaris 8 software to the Solaris 10 10/08 software, upgrade to any of the releases in the preceding list first. Then upgrade to the Solaris 10 10/08 release.