I was doing rsync over SSH - so, nothing special... just everyday work stuff.
However, trying to do this with our new Debian Squeeze server, returned the following error message:
I was pretty confused, as I first thought it did not find rsync on my machine...bash: rsync: command not found
rsync: connection unexpectedly closed (0 bytes received so far) [sender]
rsync error: remote command not found (code 127) at io.c(632) [sender=3.0.4]
[SOLUTION]
"rsync" was not installed on the new server by default.
Simply installing the package "rsync" solved it.