XP Home to Pro Upgrade problem

Good evening.

Small problem here:

While not really necessary, I wanted to update from XP Home to XP Pro for
some additional features and such and I encountered a problem.

It starts off OK: recommends upgrade rather full install which I choose,
checked for any new downloadable things for the update process (tried it this
way and also skippped that function).

I then enter the product key and it copies some things from the disk to the
hard drive and then at the very end of that process I get an error message
saying something to the effect that, "as23YTpp567.sys" is missing...would
like to retry, skip or cancel...

Itired all of those things. It will not work with a re-try, skipping result
in a error upon reboot and cancel simply stopps the install process.

I then tried booting from CD and that only allows a full install...and I do
not want that;

I tried copying the disk, thinking that sometimes if there is something
corrupt or a ding in the CD, burning sometimes corrects those issues...

nothing appears to be working.

I turned off all virus and security procotcols I have in place (Zone alarm
Pro Suite and a couple other apps)...

One thing that occurred to me is that I have shut off unnecessary services
via msconfig and other apps...more of the the annoying non essential kind
(including non-MSoft variety) but I don't recall or believe I've shut off
anything integral to XP...

Any suggestions or assistance would be appreciated.

thank you for your time and attention.

G