Q. When you attempt to start Windows XP, you receive a 0x8009001d error?

You will receive a 0x8009001d error if you modified the boot drive letter assignment or the system drive letter assignment in the HKEY_LOCAL_MACHINESYSTEMMountedDevices.

Microsoft defines the System Partition as the partition that contains the startup files, NTDetect.com, NTLDR, and Boot.ini.

Microsoft defines the Boot Partition as the partition that contains the system files (%SystemRoot%System32).

Microsoft does NOT support changing the System Partition or Boot Partition drive letters in Windows XP.

NOTE: See tip 2596 How do I change the System/Boot drive letter in Windows 2000?