Windows 8 activation error 0x8007007B.

I have the same problem. My PC (ASUS UX32VD) just came back from servicing (they replaced the motherboard and the iSSD), and after I did a system restore I'm stuck with this error :

Error: 0x8007007B 
"The file name, directory name, or volume label syntax is incorrect”

The link provided is of no help, this is a Windows 8 home edition, no KMS. And I don't have any other Windows key than the one already installed.

Did you upgrade your system to Windows 8 or did you purchase a system with Windows 8 pre-installed?

When replacing the motherboard, did you adhere to OEM licensing?

Generally, an end user can upgrade or replace all of the hardware components on a computer—except the motherboard—and still retain the license for the original Microsoft OEM operating system software.  If the motherboard is upgraded or replaced for reasons other than a defect, then a new computer has been created.

This would mean having to purchase a new license

However,  "you do not need to acquire a new operating system license for the PC as long as the replacement motherboard is the same make/model or the same manufacturer's replacement/equivalent, as defined by the manufacturer's warranty."

Try the solution given by SIV

http://social.technet.microsoft.com/Forums/en-US/w8itproinstall/thread/4615d78e-8322-42d2-ae96-634c1b61c617

Run the validation tool.  Post back the log if validation fails

http://www.microsoft.com/en-us/download/exe-validation.aspx?id=8163

1. Press Windows key + X , click Run

2. type: slui.exe 4
3. Press the ‘ENTER’ key
4. Select your Country from the list.
5. Choose the Phone Activation option.
6. Stay on the phone (do not select/press any options) and wait for a person to help you with activation.
7. Explain your problem clearly to the support person.

Did the repair service use a different product key?

To see what product key you're using,

Type CMD

Right click on CMD and select Run As Administrator

Type SLMGR /ATO

Press Enter

Note:  There is a space between SLMGR and /ATO

It will be a few seconds before the key appears

Write the key down.

Is it the same as your original key?

The filename, directory name, or volume label syntax is incorrect. (Error code 0x8007007B)

http://windows.microsoft.com/en-US/windows-8/activation-errors

1. Swipe in from the right edge of the screen, and then tap Search.
   (If you're using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, and then click Search.)

2. Enter SLUI 03 in the search box, tap or click Apps, and then tap or click SLUI 03.

3. Enter your 25–digit product key and tap or click Activate. You might be asked for an admin password or to confirm your choice.

4.  

You can find your product key on the box that the Windows DVD came in—or in an email that shows that you bought Windows. It looks like this: PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

You might try PC Reset - This will remove all personal data, apps, and settings from the PC, and reinstall Windows

Or, PC Refresh - This keeps all personal data, Metro style apps, and important settings from the PC, and reinstall Windows

Windows Product key is integrated with system BIOS hence while you are performing system factory reset it should take the product key automatically again it will depend upon your system manufacturer.

SLUI 03 doesn't solve the problem (I can only retrieve the current key from third party tools, as an OEM system it's only in the BIOS), and I already did a system restore...

You did say the unit was working until you did a System Restore, didn't you?

I didn't suggest a system restore, I suggested PC Reset

This will reinstall Windows on the unit and the key should be easy to locate using the slmgr /ato command I gave you earlier.  Be sure to write it down.

System Restore does reverses you to a previous date/time/setting

If Asus replaced the motherboard, the key quite possibly may have been changed.  They would have your Product Key information. 

What chipset is being used and is it the same as the one prior to changing the motherboard?

In 2011 ASRock, ASUSTeK, Gigabyte and MSI launched several consumer-based motherboards using the Intel 6-series LGA 1155 chipset and AMD 9 Series Chipset for AM3+ AMD FX (Bulldozer) and AMD Fusion Processors with EFI.^[36]

With the release of Windows 8 in October 2012, Microsoft's certification requirements now require that computers include firmware that implements the UEFI specification.

PC Refresh   -   Keep all personal data, Metro style apps, and important settings from the PC, and reinstall Windows

You may have to reinstall some software(s)

PC Reset - Takes the unit back to Factory defaults.