The program that needs this .sys needs to have it in System32, and depending on the OS (64/32) I have two versions of the file to copy. I'm checking @OSArch to determine which one to copy, but the script needs to run on both 32 and 64 bit systems.
My path actually is based on the Windows directory, because I also noticed that the system directory AutoIt gives is for sysWOW64. So my command is:
FileCopy(@WindowsDir & "\System32\drivers\64b.sys", @WorkingDir & "\Win64\64b.sys", 9)
FileExists(@WindowsDir & "\System32\drivers\64b.sys") returns 1, but the file is not there. It also doesn't appear in sysWOW64.