unable to sign xp driver with "official certificate"

I am developing a Windows XP USB driver. I have followed the example in the WinDDK 6000 “selfsign_example.cmd”. Using a test certificate, my driver was signed without a problem (as viewed in DeviceManager). Next I purchased a Verisign Class 3 Code Signing certificate. The selfsign_example.cmd script executes properly, signs the driver and catalog file with an authentic certificate and installs the certificate. I can individually verify both the driver and catalog file, which are signed and chained to the certificate as expected. My driver executes without a problem after installation. However when I view the driver via DeviceManager, it shows as unsigned.

In setupapi.log, all goes well until the final few lines during my driver's installation:

@ 16:31:43.080 #V155 Executing default installer.

@ 16:31:43.112 #T200 Install Device: Begin.

@ 16:31:43.128 #V124 Doing copy-only install of "USB\VID_0A28&PID_0001\5&B791E26&0&2".

@ 16:31:43.159 #V005 Opened the PNF file of "c:\windows\inf\oem4.inf" (Language = 0409).

@ 16:31:43.175 #V011 Installing section [XylocUSB.INSTALL.NT] from "c:\windows\inf\oem4.inf".

@ 16:31:43.191 #T203 Install Device: Queuing files from INF(s).

@ 16:31:43.207 #V005 Opened the PNF file of "C:\WINDOWS\INF\drvindex.inf" (Language = 0409).

@ 16:31:43.239 #V094 Queued copy from section [XylocUSB.CopyFiles] in "c:\windows\inf\oem4.inf": "XylocUSB.sys" to "XylocUSB.sys" with flags 0x00000024, target directory is "C:\WINDOWS\system32\drivers".

@ 16:31:43.255 #V095 Source in section [sourcedisksfiles] in "c:\windows\inf\oem4.inf"; Media=1 Description="XylocUSB Installation Diskette" Tag="" Path="".

@ 16:31:43.287 #T204 Install Device: Queuing coinstaller files from INF(s).

@ 16:31:43.318 #V005 Opened the PNF file of "c:\windows\inf\oem4.inf" (Language = 0409).

#-046 Processing Coinstaller registration section [XylocUSB.INSTALL.NT.CoInstallers].

@ 16:31:43.382 #V056 Coinstallers registered.

@ 16:31:43.398 #V011 Installing section [XylocUSB.INSTALL.NT.Interfaces] from "c:\windows\inf\oem4.inf".

@ 16:31:43.414 #V054 Interfaces installed.

@ 16:31:43.446 #V121 Device install of "USB\VID_0A28&PID_0001\5&B791E26&0&2" finished successfully.

@ 16:31:43.462 #T201 Install Device: End.

@ 16:31:43.493 #V156 Completed default installer.

@ 16:31:43.509 #T185 Pruning Files: Verifying catalogs/INFs.

@ 16:31:43.541 #I180 Verifying file "c:\windows\inf\oem4.inf" (key "xylocusb.inf") against catalog "oem4.CAT" failed. Error 1168: Element not found.

@ 16:31:43.557 #I180 Verifying file "c:\windows\inf\oem4.inf" (key "xylocusb.inf") against catalog "oem4.CAT" failed. Error 1168: Element not found.

@ 16:31:43.589 #T186 Pruning Files: Verifying catalogs/INFs completed.

@ 16:31:43.621 #I180 Verifying file "C:\WINDOWS\system32\DRIVERS\XylocUSB.sys" (key "XylocUSB.sys") against catalog "C:\WINDOWS\system32\CatRoot\{F750E6C3-38EE-11D1-85E5-00C04FC295EE}\xylocusb.cat" failed. Error 0x800b0110: The certificate is not valid for the requested usage.

@ 16:31:43.668 #V330 Verifying file "C:\WINDOWS\system32\DRIVERS\XylocUSB.sys" (key "XylocUSB.sys") as self-signed failed. Error 0x800b0110: The certificate is not valid for the requested usage.

Might anyone shed some light on my error and advise me as to corrective actions?

Thanks

Dan