Remember that cron runs as root and may have a different $PATH than when
you run from the console. Ensure that you use full pathnames when
referencing files. Also check the system log files for any suspicious
goings on. Next would be to insert some debugging statements in the
code to determine where it is failing. Write the debug output to a file
for later examination.

Actually cron runs jobs as whoever scheduled the job to run. In any
case, you need to properly set your path in any scripts run from cron.
Assume nothing.

The easy way: install Back in Time from the Ubuntu repositories.

What I meant to say is that cron does not set the user's $PATH (on my
systems users cannot run cron, only root) consequently a script could
run from a shell and not from cron. Most cron issues are path related.

Maybe this is just a typo in the email, but there should be no space on the
first line of your script. i.e., shoud be "#!/bin/bash", unless I am
loosing my mind (I wouldn't put that past me) :)

I don't know too much about cron, but you may want to add something like "
--log-file=/some/directory/rsync.log" to your rsync command to see if any
errors are getting thrown. But that may not help if the issue is that cron
is not able to find rsync. like if it only looks in /usr/bin and rsync is in
/usr/local/bin. But I don't know.

It worked! That's the only change I made, took out that errant space and
it ran.

Seems odd, because the script itself was running (it output its
messages) and I would have thought if it couldn't identify the shell
properly it would have failed altogether...?

I think with the space, it interpreted that first line as a comment,
and used the default shell syntax to try to interpret the script
(Bourne maybe?). It worked from the terminal, I assume, because you
were executing it from withing the bash shell. But that level of
knowledge is somewhat out of my league. Glad you got it working.