When you restart your computer during the Windows XP Service Pack 2 upgrade, you receive:

A problem has been detected and Windows has been shut down to prevent damage to your computer...
Technical information:
*** STOP: 0x00000050 (0x........, 0x........, 0x........, 0x........)
PAGE_FAULT_IN_NONPAGED_AREA

If you have the BootSkin program from Stardock Corporation enabled during the install, you may experience this behavior.

To workaround this behavior, turn off the BootSkin program before you installed SP2. When the install is complete, you can turn it back on.