The two most common reasons for this are

(1) failing to use the magic word "tenex" (when connected to SIMTEL20 and
    other TOPS20 systems) or "binary" (when connected to UNIX systems) when
    transferring the file from an ftp site to your host machine.  The
    reasons for this are technical and boring.  A synonym for "tenex" is
    "type L 8", in case your ftp doesn't know what "tenex" means.

(2) failing to use an eight-bit binary transfer protocol when transferring
    the file from the host to your PC.  Make sure to set the transfer type
    to "binary" on both your host machine and your PC.

gopher is also known to corrupt binary files. In particular, if gzip
complains about a multi-part file, it's likely that the .gz file
has been corrupted by gopher. Use ftp in binary mode instead.

Some parts © 2009 Advameg, Inc.