The ancient curl shipped with the AIX Toolbox can't handle large files.
Test case:
curl -o revelations-2.iso http://ftp.acc.umu.se/mirror/media/StarWars-Revelations/revelations-2.iso
The resulting file should be over 4GB in size, not 378 bytes.
See the directory index at http://ftp.acc.umu.se/mirror/media/StarWars-Revelations/ for MD5SUMS and more information on that particular file.