First a quick note: please upgrade Joomla! to 1.5.23 and Akeeba Backup to 3.2.7 for security reasons.
Now, try setting the temporary directory to [DEFAULT_OUTPUT] (all capital letters, brackets included) and retry a backup. If that fails, make sure you have enough free space on your hard disk. If you have older backups, make sure you remove them from your site to conserve some disk space.
If ti still fails, please ZIP and attach your new log file. Thanks!
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!