So I found a script online, took it and hacked it to pieces to fit my environment. Basically, I want to keep backups for 14 days with a full backup every 7 days. Lately I noticed the following in my logs.

2009-08-01_11:32:33: Backup for local filesystem started
2009-08-01_11:32:33: ... removing old backups
Last full backup date: Tue Jul 28 02:00:11 2009
No old backup sets found, nothing deleted.
Last full backup date: Wed Jul 29 02:00:31 2009
There are backup set(s) at time(s):
Tue Jul 14 02:07:13 2009
Wed Jul 15 02:00:31 2009
Thu Jul 16 02:00:22 2009
Fri Jul 17 02:00:28 2009
Sat Jul 18 02:00:27 2009
Which can't be deleted because newer sets depend on them.
No old backup sets found, nothing deleted.
2009-08-01_11:32:34: ... backing up filesystem
Last full backup date: Tue Jul 28 02:00:11 2009

What I've been doing is logging in S3 via the S3 plugin and deleting the old backup sets. I re-run the script and all is well. So, what's the issue?

The script was lifted from here:

http://www.cenolan.com/2008/12/how-to-incremental-daily-backups-amazon-s3-duplicity/

AFAIK that script makes an incremental backup during a certain time and during that time newer backups depends on olders.

You know, incremental

What do you have set in this line of your script?

# How long to keep backups for