Try getting the
tar.bz2 version of it, if theres a corruption during transfer, the bzip2recover should be able to recreate the lost bits.
Remember this is not a zip file, it is a tar-red achive that is compressed with gzip/bzip2 so on a *nix ssystem you'd use: tar xcf cal.tgz or tar jxf cal.tar.bz2 to uncompress it.
It will create a directory called "calender" where every file it requires resides.
If you need it in another format, let me know, and I'kll try and see if I can convert it to a zip archive tomorrow.