I didn't make it!
I uninstalled EVERYTHING, reinstalled cod then the patch. patch says pak0.pk3 is not a valid previous version & could not be upgraded. I did it cause I could not download any more mods cause pks gave issues every time.
I'm too cool to Post
22nd September 2002
Did you delete all COD folders after uninstall as well? Is this a legal copy? A quick search says there are different versions of the patch and to install them in order.
I did a search in google with this: pak0.pk3 is not a valid previous version This will also be moved to the COD forums. Good luck.