Resetting the Windows XP registry permissions can be a scary experience, but a necessary one if you cannot complete a Service Pack update because of permissions issues. Fortunately, you can install a free utility program from Microsoft and use it to reset the registry and file permissions to their default values. If you have Windows XP Professional Edition, you can reset the permissions from the command line alone.

If you are using Windows XP Professional Edition, use the SECEDIT command line program to reset registry and file system permissions.

Select "Run" from the Start Menu, then type "CMD" in the Open box and press "Enter." At the command line prompt, type:

secedit /configure /cfg %windir%\repair\secsetup.inf /dB secsetup.sdb /verbose

and press "Enter."

This resets the registry and file permissions.

If you are using Windows XP Home Edition, download the subinacl.msi file from Microsoft. (See the Resources section for the download location.)

Double-click the subinacl.msi file to obtain the subinacl.exe file, then double-click the subinacl.exe file.

Select "Run" from the Start Menu, then type CMD in the Open box and press "Enter." At the command line prompt:

Type cd /d "%ProgramFiles%\Windows Resource Kits\Tools" and press "Enter."

Type subinacl /subkeyreg HKEY_LOCAL_MACHINE /grant=administrators=f /grant=system=f and press "Enter."

Type subinacl /subkeyreg HKEY_CURRENT_USER /grant=administrators=f /grant=system=f and press "Enter."

Type subinacl /subkeyreg HKEY_CLASSES_ROOT /grant=administrators=f /grant=system=f and press "Enter."

Type subinacl /subdirectories %SystemDrive%\ /grant=administrators=f /grant=system=f and press "Enter."

This sequence resets the registry and file permissions.