WinUSB driver installation failing on XP (works fine on Win7)

I'm having difficulty installing a WinUSB driver on Windows XP (x86, service pack 3). I've followed the Microsoft WinUSB guidelines to create a signed driver package using an inf file, signed cat file (made using Inf2cat), and relevant WinUSB coinstallers. Everything works perfectly on Windows7, but installation fails on XP.

The inf file is as follows:

[Version]
Signature = "$Windows NT$"
Class = "Digitool Processors"
ClassGuid={D851949D-3793-4FA6-93F5-E86CCDCFD6F9}
Provider = %ProviderName%
CatalogFile=DigitoolCatFile.cat
DriverVer=10/28/2010,1.0.0.0

; ================== Class section ==================

[ClassInstall32]
Addreg=MyDeviceClassReg

[MyDeviceClassReg]
HKR,,,0,%ClassName%
HKR,,Icon,,-1

; ========== Manufacturer/Models sections ===========

[Manufacturer]
%ProviderName% = Digitool_WinUSB,NTx86,NTamd64,NTia64

[Digitool_WinUSB.NTx86]
%USB\MyDevice.DeviceDesc% =USB_Install, USB\VID_064B&PID_1212

[Digitool_WinUSB.NTamd64]
%USB\MyDevice.DeviceDesc% =USB_Install, USB\VID_064B&PID_1212

[Digitool_WinUSB.NTia64]
%USB\MyDevice.DeviceDesc% =USB_Install, USB\VID_064B&PID_1212
; =================== Installation ===================

[USB_Install]
Include=winusb.inf
Needs=WINUSB.NT

;[2]
[USB_Install.Services]
Include=winusb.inf
Needs=WINUSB.NT.Services

;[3]
[USB_Install.Wdf]
KmdfService=WINUSB, WinUSB_Install

[WinUSB_Install]
KmdfLibraryVersion=1.9

;[4]
[USB_Install.HW]
AddReg=Dev_AddReg

[Dev_AddReg]
HKR,,DeviceInterfaceGUIDs,0x10000,"{40F2F474-A52F-4DDD-815F-785DFA5A5550}"

;[5]
[USB_Install.CoInstallers]   
AddReg=CoInstallers_AddReg
CopyFiles=CoInstallers_CopyFiles

[CoInstallers_AddReg]
HKR,,CoInstallers32,0x00010000,"WdfCoInstaller01009.dll,WdfCoInstaller","WinUSBCoInstaller2.dll"

[CoInstallers_CopyFiles]
WinUSBCoInstaller2.dll
WdfCoInstaller01009.dll

[DestinationDirs]
CoInstallers_CopyFiles=11

; ================= Source Media Section =====================
;[7]

[SourceDisksNames]
1 = %DISK_NAME%,,,\i386
2 = %DISK_NAME%,,,\amd64
3 = %DISK_NAME%,,,\ia64

[SourceDisksFiles.x86]
WinUSBCoInstaller2.dll=1
WdfCoInstaller01009.dll=1

[SourceDisksFiles.NTamd64]
WinUSBCoInstaller2.dll=2
WdfCoInstaller01009.dll=2

[SourceDisksFiles.ia64]
WinUSBCoInstaller2.dll=3
WdfCoInstaller01009.dll=3
; =================== Strings ===================

[Strings]
ProviderName="Peavey Electronics"
USB\MyDevice.DeviceDesc="Digitool USB"
WinUSB_SvcDesc="Digitool USB"
DISK_NAME="Install Disk"
ClassName="Digitool Processors"

The setupapi log on failure in XP looks like this:

[SetupAPI Log]
OS Version = 5.1.2600 Service Pack 3
Platform ID = 2 (NT)
Service Pack = 3.0
Suite = 0x0100
Product Type = 1
Architecture = x86
[2011/10/28 18:33:56 5900.645]
#-198 Command line processed: "C:\WINDOWS\system32\mmc.exe" C:\WINDOWS\system32    \devmgmt.msc /s 
#I060 Set selected driver.
#-019 Searching for hardware ID(s): usb\vid_064b&pid_1212&rev_0100,us \vid_064b&pid_1212
#-018 Searching for compatible ID(s): usb\class_ff&subclass_00&prot_00,us \class_ff&subclass_00,usb\class_ff
#I022 Found "USB\VID_064B&PID_1212" in C:\WINDOWS\inf\oem34.inf; Device: "Digitool USB"; Driver: "Digitool USB"; Provider: "Peavey Electronics"; Mfg: "Peavey Electronics"; Section name: "USB_Install".
#I087 Driver node not trusted, rank changed from 0x00000001 to 0x00008001.
#I023 Actual install section: [USB_Install]. Rank: 0x00008001. Effective driver date: 10/28/2010.
#-166 Device install function: DIF_SELECTBESTCOMPATDRV.
#I063 Selected driver installs from section [USB_Install] in "c:\windows\inf\oem34.inf".
#I320 Class GUID of device remains: {D851949D-3793-4FA6-93F5-E86CCDCFD6F9}.
#I060 Set selected driver.
#I058 Selected best compatible driver.
#-124 Doing copy-only install of "USB\VID_064B&PID_1212\5&26DFC3A5&0&2".
#W334 Failed to verify catalog when scanning file queue. Error 1168: Element not found.
#E360 An unsigned or incorrectly signed file "c:\windows\inf\oem34.inf" for driver "Digitool USB" will be installed (Policy=Ignore). Error 1168: Element not found.
#W187 Install failed, attempting to restore original files.
#E360 An unsigned or incorrectly signed file "c:\windows\inf\oem34.inf" for driver "Digitool USB" will be installed (Policy=Ignore). Error 1168: Element not found.
#-024 Copying file "C:\WINDOWS\system32\DRVSTORE\digitool_AB7D48D412FA027D36DB13E9FD73698685B0025A\i386\WinUSBCoInstaller2.dll" to "C:\WINDOWS\system32\WinUSBCoInstaller2.dll".
#E360 An unsigned or incorrectly signed file "C:\WINDOWS\system32\DRVSTORE\digitool_AB7D48D412FA027D36DB13E9FD73698685B0025A\i386\WinUSBCoInstaller2.dll" for driver "Digitool USB" will be installed (Policy=Ignore). Error 1168: Element not found.
#-336 Copying file "C:\WINDOWS\system32\DRVSTORE\digitool_AB7D48D412FA027D36DB13E9FD73698685B0025A\i386\WdfCoInstaller01009.dll" to "C:\WINDOWS\system32\WdfCoInstaller01009.dll" via temporary file "C:\WINDOWS\system32\SET15.tmp".
#E360 An unsigned or incorrectly signed file "C:\WINDOWS\system32\DRVSTORE\digitool_AB7D48D412FA027D36DB13E9FD73698685B0025A\i386\WdfCoInstaller01009.dll" for driver "Digitool USB" will be installed (Policy=Ignore). Error 1168: Element not found.
#-166 Device install function: DIF_REGISTER_COINSTALLERS.
#I056 Coinstallers registered.
#-166 Device install function: DIF_INSTALLINTERFACES.
#-011 Installing section [USB_Install.Interfaces] from "c:\windows\inf\oem34.inf".
#I054 Interfaces installed.
#-166 Device install function: DIF_INSTALLDEVICE.
#I123 Doing full install of "USB\VID_064B&PID_1212\5&26DFC3A5&0&2".
#E275 Error while installing services. Error 0xe0000219: The installation failed because a function driver was not specified for this device instance.
#E122 Device install failed. Error 0xe0000219: The installation failed because a function driver was not specified for this device instance.
#E157 Default installer failed. Error 0xe0000219: The installation failed because a function driver was not specified for this device instance.
#W422 Coinstaller 1 (Post Processing) modified status. Error 87: The parameter is incorrect.
#I060 Set selected driver.
#I125 Installing NULL driver for "USB\VID_064B&PID_1212\5&26DFC3A5&0&2".
#I121 Device install of "USB\VID_064B&PID_1212\5&26DFC3A5&0&2" finished successfully.

I'm tearing my hair out trying to figure out what's going wrong on XP. The errors

"Failed to verify catalog when scanning file queue" and "An unsigned or incorrectly signed file"

make no sense to me, as the driver package is correctly signed, and installs correctly on Win7 with no warnings. Any help would be extremely welcome

Thanks Tom

One issue I believe is that [SourceDisksFiles.NTamd64] should be [SourceDisksFiles.amd64]. I'm not sure that is the issue, but thats one problem.

I think the real issue is that Windows XP does not support this line: Needs=WINUSB.NT.Services

You need to change it to this:

;[2]
[USB_Install.Services]
Include=winusb.inf
Needs=WinUSB,0x00000002,WinUSB_ServiceInstall

[WinUSB_ServiceInstall]
DisplayName = %DisplayName% ; set this in your string area
ServiceType = 1
StartType = 3
ErrorControl = 1
ServiceBinary = %12%\WinUSB.sys