This is a problem I was having (see previous post) after upgrading to 10.4.3. Well, I’m finally up and running 10.4.5 and seem to have eliminated the issue (so far). I’d like to describe my solution for others having the problem (see my original post for background info).
I believe the problem has to do with using the Migration Assistant--specifically, the option to move over Files and Folders at the root level, so I recommend leaving this option unchecked during your migration. As a matter of fact, leave anything you can absolutely do without unselected to minimize the chance of corrupting your new system during migration.
The first thing I did was install and upgrade completely (from 10.4.2. to 10.4.5. using the Combo installer and the Software Update panel to get it all up to speed). Then, after repairing permissions, I manually installed every kernel extension I could think of (i.e., xxx.kext) that I thought I would use; this way, no extensions would be installed via the migration from Panther to Tiger. After getting to this point (with a system that would restart fine every time), I made a backup using SuperDuper just in case I had to go back to square one.
Finally, I proceeded to use Migration Assistant, but I did not migrate root-level files and folders, and I also didn’t migrate my network settings. Everything else migrated fine, and I’ve noticed no major differences so far (except that Tiger is much snappier on my system than Panther was). So far, the dreaded, sneaky gray-Apple-screen-of-death issue has been averted. I don’t know why or exactly how, but for those of you having this problem, you should attempt this fix in the Migration Assistant. Better yet, don’t use it all and start over from the beginning (manually copying over stuff you need).
Again, my issue is different from some others in that I was migrating on the same computer...on old, heavily-upgraded G4 AGP Mac. All seems great right now...