Q: How to fix bad plist?

I don't know what your issue is with this computer, so I cannot say if this will change anything. It would really help if you explained what happens when you boot & what errors or problems it has. Simply assuming this T.T.P. diagnosis is correct is a longshot in my opinion.

You could probably just take a copy of the entire system & 'migrate' the user account to access the mail or contacts on another Mac. Target Disk Mode can be used to make a non booting Mac's disk readable on another computer for example. You can also dig into her account & find the mail or contacts manually.

How to use and troubleshoot FireWire target disk mode - Apple Support – you need approbate cables to make use of this mode.

You could obviously delete or just move the plist - I dare say TechTool Pro will have an option to do that somewhere in it's fix or repair sections?

That plist manages lots of network & system level settings, so the OS will recreate it with default values after you remove it & reboot. I'd suggest you move the file to a new location & reboot incase you need to restore it. TTP may simply be finding an error where non exists (I have had it do that for me in the past - making a Mac unbootable!).

What state is the Mac in? Can you get to a user login? Is your only aim to access the user data?

Whew, in 10..5 here the first few lines are...

<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">

<plist version="1.0">

<dict>

  <key>CurrentSet</key>

  <string>/Sets/1FC50A8D-0376-4BFD-87F7-F2A9CEFF72CF</string>

  <key>NetworkServices</key>

  <dict>

  <key>21CB8D15-9878-4549-83F7-E9D20FE592BC</key>

  <dict>

  <key>DNS</key>

  <dict/>

  <key>IPv4</key>

  <dict>

  <key>ConfigMethod</key>

  <string>DHCP</string>

Have you booted up to the Restore Partition holding CMD+r & used Disk Utility to Repair Disk?

Click on go > computer > macintosh HD > preferences > system configuration > remove  preferences.plist to the desktop .Then go  into the recovery mode > disk utility > click on repair disk , to enter into recovery mode an apple article is there : OS X: About OS X Recovery - Apple Support

appreciate wrote: Click on go > computer > macintosh HD > preferences > system configuration > remove  preferences.plist to the desktop .Then go  into the recovery mode > disk utility > click on repair disk....

1. That won't go anywhere. Go to Folder (CMD-Shift-G) requires the Unix path:

/Library/Preferences/SystemConfiguration/preferences.plist

2. Instead of moving the .plist to the Desktop, which will change the ownership of that folder incorrectly to the user, right-click>Move to Trash. You will be asked for your admin password. Don't empty the Trash.

3. Next, to get a new default .plist, log out and back in, or restart. Live with that new one for a while (the one you trashed contains preferences which may need to be recreated) or run a new TTP. If TTP comes up with the same error, then just forget about it.

4. If needed, the .plist in the Trash can be returned to its original location, with the option to replace the the new one, by highlighting the .plist in the Trash, right-click> "Put Back." You will again be asked for your admin password.

Also, not at all certain that this is related to the Disk directory structure, so Repair Disk may not do anything for this issue. In fact, what I would try first, with all Applications closed, is Disk Utility (Applications> Utilities)> Verify Disk. No need to boot into Recovery Mode for this. If it comes up with no errors, then forget about doing Repair Disk.

Note: since this may be specific to your particular configuration, this doesn't have to mean anything at all, but I do not have >com_apple_ats_name_fond.Description</key> anywhere in that .plist in my Mountain Lion.

I'm glad you got what you were looking for

Did you use target disk mode to get at it?