Ubuntu :: Called 'backit' - To Back Up Files To A Tarball?

I have a script - called 'backit' - to back up files to a tarball - listed below (<backup.lst> contains files I want backed up)

#!/bin/bash
# 22/7/2010
# Backup important files
cd ~
tar cvfz .backup/backup.tar.gz -T .backup/backup.lst
cp .backup/backup.tar.gz /media/Archive/.backup

Typing 'Backit' in the shell works very well producing a backup file, <backup.tar.gz>, of 2 298 953 bytes and contains all the correct files. So far, so good! I put a line in crontab - /home/alan/bin/backit

The program runs every hour on the hour and produces the <backup.tar.gz> file. However, this file contains only some of the files and has a size of 76 762 bytes. Using "tar tvf backup.tar.gz" lists some of the files and ends with an error indicating an EOF encountered before the end of file. If the script executes correctly when typed into the shell, why does it not run to completion correctly when run by cron?