rsync - Dec 2001 - unexplained error code when updating large (2G+) file

When trying to transfer a large file to another system in update mode
(actually checking new build of 2.5.0 on HPUX 11.11, the file already exists
but I was checking to see that rsync recognized that), I get:

rsync error: unexplained error (code 130) at main.c(537)

Any suggestions as to what and where the problem might be?