As we all know Microsoft has released the final version of Windows XP SP3 to public and its available via Automatic Updates, Windows Updates and Downloads Center.
Earlier we posted about it at following link:
Windows XP SP3 RTM Available on Windows Update, Automatic Update and Download Center
You can download the SP3 from the above mentioned link.

I have received a few mails mentioning a strange problem which occurs while installing SP3 in Windows XP. A few people told me that whenever they try to install SP3 in Windows XP, Windows shows following error message:
Service pack 3 setup cannot update a checked (debug) system with a free (retail) version of service pack 3, or vice versa.

The reason behind this problem is that the update package installs retail bits on retail builds and checked bits on checked builds. But you can spoof Windows updates in order to install retail bits on checked builds and vice versa.
If you are also facing the same problem, then follow these simple steps and your problem should be solved:
1. Type regedit in RUN dialog box and press Enter. Now goto:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion
2. In right-side pane look for a String value "CurrentType". Change its value to Checked and if its already set to Checked, then set it to Free and click on OK.
3. Exit registry editor and try to install SP3 again. Now it should install without any problem.
This article was posted by VG in following section: Troubleshooting, Windows XP.
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Jeet
Thank you so much VG. I was facing the exact prob and your solution worked perfectly. You are a true genius.
Neo
I have seen many people in forums facing this problem. I'll let them know about your solution. Thanks for it.
Kelly
Yep. It works. My special thnx to you VG
Minu
Mine was set to free and I changed it to checked and it worked.
You are gr88888 VG
Omi Azad
I found this problem on another forum. I went to install SP3 on my office computers and none of them installed successfully. I think this happened because of OEM versions.
Ramesh
you hav done the gr8 job.
Tone
I tried that...didn't work. Same error came up. Would you happen to have any other solutions? Thanks in advance.
Charlie
I tried your solution and received the same error message. When I checked the registry after reboot the value was reset. It actually says Unicore Free. I did not change the Unicore just the free.
Lucas
# Charlie
Change the value od CurrentType and install the Service Pack, don't restart you PC. Then it will work, good luck!
Lucas
son
Hi
my computer has: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\currentType = Multiprocessor Free;
I tried but not change and cannot upgrade sp3.
Help me please