There are a couple different forms of SP2. Microsoft mailed SP2 to registered corporate customers many years ago and I got 2 of them. My guess is that its looking for a target file on that CD and there is a naming mismatch of some kind. For SP2 there is the Microsoft update method as well as the System Admin Network install of SP2, as well as the SP2 CD that Microsoft mailed out to registered corporate customers who requested the CD.
It might be a matter of making sure the SP2 file is a specific file name and not a variant such as the Network System Admin SP2 download might be a different named EXE than the service pack 2 exe that came on the CD. Matching the file names might be the fix.
Lastly... if this is a bootleg of XP 64bit it could be broken in which it will never find SP2. If this is the case then you need to get a legal copy of XP 64bit off of ebay etc.