I recently installed Ubuntu 12.10 (non server) but desire to run some server type aps.  In looking for a centralized backup solution I settled on BackupPC.  Not being a unix expert I figured having the GUI would help.  Well I have a few issues!

The good:
The bad:
travis@TAS-Server:~$ su backuppc
Password: 
su: Authentication failure
travis@TAS-Server:~$ htpasswd /etc/backuppc/htpasswd backuppc
htpasswd: cannot open file /etc/backuppc/htpasswd for read/write access
travis@TAS-Server:~$ 
Thanks for any and all help.  Once this is setup I know it is going to "just work".  Just need to learn these base issues and don't want to screw things up.  I did try to add my user to the backuppc group, but the group only has access permissions.  Before I go messing things up (again) looking for advice.

Travis