Citadel 1 of 2 will only download as Citadel 2 of 2

I bought and downloaded Citadel 1 of 2, then downloaded the free 2 of 2. I then ran into the error where it says that part 1 is an incomplete download. So I deleted both parts 1 and 2 (to avoid that 1% to 5% to 100%  jump when downloading part 1 with part 2 already being on the hard drive). Now, when I finish my download(s) of part 1 it shows up in my system memory as only Citadel 2 of 2 being downloaded and installed (again I reiterate that both Citadel 1 and 2 were deleted from the drive and I'm only downloading part 1 at this time). I deleted the file and tried again thinking I inadvertently selected the wrong part. But, this issue keeps reoccuring. I've run out of ways to troubleshoot this problem. Any help would be appreciated.