rsync+stunnel

Hello,

1. I am successfully executing rsync with stunnel in a script as root:

[...]
stunnel -c -d localhost:45873 -r rsync.ibackup.com:5000

nice -n10 /usr/bin/rsync -r -t --delete-after --password-file=[password
file] /home/offsite/files/ [my remote account]@localhost::ibackup
--port=45873

killall stunnel
[...]


2. I would like to execute the rsync command within this script as user
"offsite" for extra security:

[...]
stunnel -c -d localhost:45873 -r rsync.ibackup.com:5000

su -s /bin/bash -c "nice -n10 /usr/bin/rsync -r -t --delete-after
--password-file=[password file] /home/offsite/files/ [my remote
account]@localhost::ibackup --port=45873" offsite

killall stunnel
[...]

but I get the following error:

rsync: pop_dir "/home/offsite/files" failed: Permission denied (13)
rsync error: errors selecting input/output files, dirs (code 3) at
flist.c(1226)

all folders and files including the password file under /home/offsite
are owned by user "offsite". What am I missing?

Thanks,

David