Sorry, I thought the description field would be viewable. Here are the errors I see in the Joomlapack log:

Failed Smart algorithm on JoomlapackCUBEDomainDBBackup
Could not open /path/to/Joomla/tmp/9a5201cc for append, in DB dump.

The weird part is that the file exists, so I know the application can write to that directory. Not sure why it can't open the file after it's created. It has 777 permissions by default.

Thanks a lot for your quick reply. I know just what you're talking about. After the first failed attempt, I was prompted with a yellow brick message about how I should try more "stable" (?? I forget the wording) settings and I can apply them if I want. When I did that, it prepended the TMP path with that <root> tag, got rid of the server's root path, but it still didn't work. I assume that tag is just a variable defined by Joomla which is really just the path to the Joomla installation. Six of one, half dozen of the other. If the path were the problem, I'd have to imagine Jbackup wouldn't be able to even create that tmp file, but it does every time. Very strange!

I think I may try your idea of going with a different version. I'm working on this for a friend, though, so I'm not too familiar with your software. Which version would you recommend? Joomla is version 1.5.15 Stable. Thanks again for your help!

JoomlaPack would actually change some of the magic numbers to make the backup "slower and surer".  There were two step downs after failed backups were detected.

Development has stopped on JoomlaPack completely, and officially it is unsupported.  Development continues at its frantic pace with Akeeba, the 3.1 beta is just around the corner.  The major change in requirements is that Akeeba won't run on php4.