I've just spent an hour on the phone with a good friend who has been plagued by Leopard's blue screen restart problem. Apple has issued advice but left out a critical slice of information - here it is.

The problem is as follows: After completing an upgrade installation of Leopard and restarting the computer, a "blue screen" may appear for an extended period of time.

(Let's leave aside cheap shots about how Apple and Microsoft now share yet another OS "feature", the eponymous 'blue screen of death'.)

Apple suggests the problem may stem from third-party enhancement software, such as that provided by Unsanity Software. The latter firm denies this, but has admitted earlier versions of its software may be implicated.

Apple recommends most users reinstall Leopard - but as my friend found, that's hard to do when your Mac won't restart and your Leopard install disc is no longer in the optical drive. How do you get the DVD into that drive when the Mac won't start.

This leaves users with option two - using the command line to remove the pesky application enhancement software.

Apple has published the code that must be executed in Terminal when a user launches their Mac in single-use mode (which you invoke using Command (the fabled "Apple key") while holding down the S button.

Working with my friend, we noted that the code published on Apple's site contains blank spaces - logical to Terminal habitues, but not anyone else.

My friend had been entering the code correctly, but had sometimes ignored the space.

This implies that inaccurate code entry is leaving many users stuck in an endless cycle of frustration as they attempt to get their old Mac back in order to check what their new one does.

This is the code:

"Execute these commands, each on a single line:
/sbin/fsck -fy
/sbin/mount -uw /

Please note the spaces in the code as given - particularly that clear blank space before the final backspace. Failing to do this means the commands won't work.
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Apple then advises users enter the following command - again, it's essential that any spaces are replicated in the code you enter - and be warned, as Apple states: "Type the command carefully, misuse of rm may damage other files."

rm -rf /System/Library/SystemConfiguration/ApplicationEnhancer.bundle

Once again, note the space between the first two and third character, and between the fifth and sixth character. And use capitalisation as shown above.

Then Apple blows it. "Restart normally" it advises. Which of course you can't do as your Mac still isn't working correctly.

Many users will run to the power button to achieve this.

However, restarting by switching off the power has left many users disappointed, including my mate. It means the Terminal commands won't take effect.

So we found this code to enter into Terminal, which should restart your Mac "normally", and enable you to get the machine going once again.

sudo shutdown -r now

Once again, watch out for the spaces.

Now - I can't guarantee this fix will work effectively, and can't pretend to be a Terminal power user - I'm hopeful some such users will hang by this blog entry and offer their advice in the comments field below.

However, this fix has worked for my friend, who has got his Mac Pro working again using this, though he observes that it seems to be running a little more slowly.

So - Apple should update the tech note with the relevant code to cause your Mac to restart when entering the code in Terminal.

If you have been affected by the blue screen issue, I do hope this is the missing link that gets your Mac going again. If you work for Apple, or have been affected and have managed to get things moving again, I'd appreciate you adding your input into the comments below.

Hopefully Apple will act fast to sort this problem out, meanwhile I hope this helps a little.