rdiff-backup root@<REMOTESERVER>::/apps/myapp/shared/system /home/backups/system
echo "$(date): Completed... removing backup data older than 4 weeks"
rdiff-backup --remove-older-than 4W /home/backups/system
echo "$(date): Completed..."

Fatal Error: Found 81 relevant increments, dated:
Wed Aug 29 00:41:47 2012
Thu Aug 30 00:57:49 2012
Fri Aug 31 01:04:03 2012
Sat Sep  1 00:44:59 2012
Sun Sep  2 00:41:49 2012
Mon Sep  3 00:41:39 2012
If you want to delete multiple increments in this way, use the --force.