I would say that there is a good possibility there is nothing wrong with your registry file in spite of what the error message says.
The usual problem is that XP just can't find the file due to some corruption in your NT File System (NTFS). You can usually fix this by running a chkdsk with error correction from the XP Recovery Console so I would start there.
Was the issue preceded by a power interruption, aborted restart, or improper shutdown? (this includes plug pulling, power buttons, removing the battery, etc.)
You might want to read through this thread/topic:
http://answers.microsoft.com/en-us/windows/forum/windows_xp-system/after-windows-restart-and-then-no-configsystem/83d5c57f-9836-4f3a-bec8-04c7d81861d3
You can entertain those Microsoft engaged Support Engineer "expert" ideas, but I will bet you the Microsoft engaged Support Engineer "expert" has never fixed this problem in his life, has not bothered to try to reproduce the problem and has therefore not tested
these "Methods" to see if they work or if they help.
I would also recommend that you never, never, never start with KB307545 when you have this problem and I have never used KB30745 to fix this problem in my life and somebody please shoot me dead if I ever suggest it (for this problem).
Those ideas come from zero practical troubleshooting experience and are just guesses and links to KB articles, but do try them if you are compelled to do so.
What you should to is tell us more about your system:
Since even the latest Microsoft Answers forum implementation STILL does not prompt for any kind of system information when a new question is asked, we know absolutely nothing about your system. Not knowing fundamental information about a problem prolongs the
frustration and agony of resolving these issues.
Thank you MS Answers, for continuing to make the resolution of simple problems as frustrating and time consuming as possible.
Please provide additional information about your system as best you can:
What is your system make and model?
What is your XP Version and Service Pack?
Does your system have IDE drives or SATA drives?
Describe your current antivirus and anti malware situation: McAfee, Symantec, Norton, Spybot, AVG, Avira!, MSE, Panda, Trend Micro, CA, Defender, ZoneAlarm, PC Tools, Comodo, etc.
Was the issue preceded by a power interruption, aborted restart, or improper shutdown? (this includes plug pulling, power buttons, removing the battery, etc.)
Does the afflicted system have a working CD/DVD drive (internal or external)?
Do you have a genuine bootable XP installation CD that is the same Service Pack as your installed Service Pack (this is not the same as any Recovery CDs that came with your system)?
If the system used to work properly, what do you think might have changed since the last time it did work properly?