Cannot install Snow Leopard over 10.5.8 because "can't boot from" boot disk

Can the affected user in this thread please use Disk Utility to look at the partition of their HD and let me know if they see a small 100 MB or so sized partition in addition to your boot partition. To do this, launch Disk Utility > Highlight the HD (not the Macintosh HD the one above) then click on the Partition tab. You will then see the partitions on your HD. Thanks.

same thing on my Macbook Air 😟 won't install, no matter what I do

well, did an extensive disk-cleaning using Onyx. To no avail. Since using a networked drive to boot from has never worked on this particular Macbook Air, I guess I'm screwed - I couldn't even do a clean install if I wanted to. I'm taking this thing to the nearest Apple Store and have them do the upgrade for me, I guess.

Are there any affected users on this thread that do not have PGP desktop installed? Thanks.

@gicmo: I don't have PGP, never had it. I also haven't used the Macbook Air with Time Backup, there's no backup.backupdb. The partition is GUID and I don't have a small left-over partition, either. It's a 128gb SSD drive, if that's relevant.
Don't know what the heck is going on 😟

Hmm, perhaps we misinterpreted something here - perhaps by "disk" they don't mean the harddrive but the Snow Leopard medium. I just discovered that it says "Mac Pro" on the sticker (the one that was on the cellophane wrap). Could it be that Apple is selling computer-specific versions of Snow Leopard to random customers without asking which version they need? Just a thought, though - I hope I'm wrong.

No PGP (whatever it is!) here.

My Boot drive has two partitions, GUID all working fine. the first partition was my working boot volume. The second partition was a Superduper clone of the first.

Snow Leopard was quite happy to install on the clone but not on my main working volume.

I have now installed Snow on the clone and clone it back to the main boot volume. All seems well so far, very early days.

This is replicable on my factory spec (e.g. no new hardware in it) MBP. I also had PGP desktop installed with no additional partitions and not using whole disc encryption (as it's not part of the type I have) nor PGPDisk.

Ran Disk Utility, repair disk, repair disk permissions
Uninstalled PGP Desktop (PGP Desktop -> app menu -> Uninstall)

*RESTART MACHINE*

I was then able to select the drive. Not sure why the presence of PGP desktop or it's processes causes this, but it's repplicable

hmm, coming to speak of it - I have GnuPG installed. Don't see how that would do anything but I guess I'll try to uninstall it and give it another shot.

I was just able to fix the issue on my Macbook Air: I used the bootcamp utility to add a 5gb Windows partition. After that, the installer works! Will be removing the 2nd partition once the upgrade is done.

Hope this works for you guys as well!

This happening on my iMac Core 2 Duo (2.8GHz, 2GB RAM).
I had PGP installed on it, but only to read external drives that were encrypted. This drive has never been encrypted. I uninstalled PGP, repaired permissions and the Disk. I can boot from the 10.6 DVD and run repairs from it. But when it runs the Repair Disk option, below where it says Repair Complete, it says "Updating boot support partitions for the volume as required." Odd. There is nothing to indicate that it is an ongoing thing, no progress bar, nothing else. But even after running Repair Disk twice, the installer still tells me that it can't install on my disk.

@John - have you tried the Bootcamp method?

I uninstalled PGP>

just to check: did you just throw it away, or did you uninstall it with the routine the program offers? start porgram, PGP-uninstall?

When I try the "bootcamp method" I get:
The startup disk cannot be partitioned or restored to a single partition.
The startup disk must be formatted as a single Mac OS Extended (Journaled) volume or already partitioned by Boot Camp Assistant for installing Windows.
This disk has never been partitioned. It is 750Gb with 77GB free. I do have a local iDisk on the machine, but that is all.

On the plus side, I could copy and paste the error message from the Boot Camp Assistant box.

I first chose "purge boot caches" or some such item from the PGP icon on the right side of the menu bar. Then I launched PGP and ran the uninstall utility from its file menu.