> try
> su backuppc -c id
> what is your output?

server:/ # su backuppc -c id
uid=105(backuppc) gid=105(backuppc) gruppi=16(dialout),33(video),105(backuppc)

> did you create the user backuppc?  if so, does backuppc have a home
> directory and does it have a default shell of /bin/bash?

Yes:
server:/ # grep backuppc /etc/passwd
backuppc:x:105:105:BackupPC,,,:/var/lib/backuppc:/bin/sh

> what is the output of
> su backuppc -c " /usr/local/backuppc/bin
>  /BackupPC -d"

The same output:
server:/ # su backuppc -c "/usr/local/backuppc/bin/BackupPC -d"
/usr/local/backuppc/bin/BackupPC: Wrong user: my userid is 0, instead
of 105 (backuppc)
Please su backuppc first
BackupPC::Lib->new failed

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