Install error : disk cannot be used to start up your computer [or] MediaKit reports partition (Map) too small

Question

Greetings,
I am aware that this problem has been discussed, but in long and vague discussions that I had to sift deeply to find an answer. Therefore I am posting a clear message, as this problem can be very troublesome for someone who just received a Mac OS installation disk and cannot install it.
Situation : you cannot install/update your new system because the installer does not consider your volume.
Error message : this disk cannot be used to start up your computer.
Version française : Ce disque ne peut pas être configuré pour démarrer votre ordinateur.
Also discussed below error: "MediaKit reports partition (Map) too small"
Note : although this occurred with a Snow Leopard (10.6) install DVD, it can alo occur with Lion (10.7) according to discussions on Apple web site.
IF YOUR CONDITIONS ARE AS FOLLOWS :
- You are using an official Apple installation DVD of Mac OS 10.6 (Snow Leopard) [or 10.7 Lion] or an official download/upgrade of those systems.
- Your main Mac partition scheme is in GUID as it should be (check with Disk Utility). That partition contains a Mac system that can start-up.
- Your volume format is: Mac OS Extended (journaled) [the format should not be Case Sensitive.]
- You have the hardware requirements to install Mac OS 10.6 (Intel processor; internal or external DVD drive or a linked DVD drive; 1 GB of RAM; a screen controlled by your computer graphics card; at least 5 GB space on the hard disk or 7 GB if you install all components).
- Using Disk Utility, you of course tried the disk Repair Tool and the Repair Permissions tool.
- Your hard disk does not have a file called Backups.backupdb (if it does, this means Time Machine has once used this hard disk for its back-ups). Anyhow, if it were the case, the installation would give a different error message (with the word TimeMachine). This file may block the installation: Apple Support suggest to place it in the garbage, *without* deleting it, and placing it back on the disk later. Mind you, if you do not use this hard disk as such to save your Time Machine back-ups, you can simply delete this file.
HOW TO FIX :
1. Boot with the 10.6 install DVD (Tip: you can either select Mac 10.6 as the boot DVD in your Start-up Preferences or simply press down c during the start-up).
2. Above the install screen, you have a Utilities tab from where you can run Disk Utility. Select your hard disk and select the Partition tab. Resize the primary Mac partition (don't add a new one) by decreasing it by about 5 GB.
It will look like this http://i.imgur.com/jHTbr.jpg
( That image shows only one partition, but the same principle applies even if you have two or more partitions on your disk.)
Also see the official Apple how to: http://support.apple.com/kb/TS3926
Version française: http://support.apple.com/kb/TS3926?viewlocale=fr_FR
3. Commit the change by hitting "Apply"
3.b. If you get the error "MediaKit reports partition (Map) too small", this is a rare error where the partition that follows (for example Bootcamp) is slightly overlapping your main Mac partition. You will need to reduce that other following partition. Once you have reduced the other partition, you will probably need to return to step 2 and 3 and try again.
[ For example, in my case, I had resized my Bootcamp with CampTune software and it would seem that the file system ended-up somehow larger than the actual partition container. I simply asked CampTune to reduce the partition a bit (barely 2 GB) and that fixed it.]
4. Reboot, again into the 10.6 install DVD.
5. You can then install 10.6.
6. Once 10.6 is installed, use the Disk Utility on the desktop (you can boot into the primary HD at this point) to resize the primary partition back to its original or maximum size.
SOURCE (main fix): http://forums.macrumors.com/showthread.php?t=774410 [and] http://support.apple.com/kb/TS3926
SOURCE (explaination for MediaKit error): some Apple discussion post.
nb: in my case, it was on a MacBook Pro (late 2008).

Answer 1

GasMan4932 wrote:
When I click on the icon for this drive, the warning message below states "Mac OS X cannot be installed on 'iMac HD', because this disk cannot be used to start up your computer." Obviously that's not true, since that's where the OS is installed.
How did you partition this drive, if you did that? Does it contain start up or utility partitions for any other OS (for instance Linux)? There have been reports that the "cannot be used to start up your computer" message will appear if a third party utility was used to create a 'triple boot' system or such, apparently because SL is picky about the format GUID partition scheme table info & how partitions are allocated space on the drive by other formatting/partition methods.
For some users with these partitions, the fix has been as simple as "tickling" (slightly changing) the partition size of some partition with Disk Utility, which apparently updates the GUID partition scheme table info so that the SL installer accepts it as safe to use with SL.( In this sense, the message may be trying to say the installer thinks the disk can't be used to reliably start up your computer with SL, not in general.)
See the discussions topic Cannot install Snow Leopard over 10.5.8 for more about this.