Comment 7 for bug 445154

Some relevant details for my system, in case it helps:

dpkg.log:

2009-10-17 12:19:14 configure backuppc 3.1.0-4ubuntu1.1 3.1.0-4ubuntu1.1
2009-10-17 12:19:14 status half-configured backuppc 3.1.0-4ubuntu1.1
...
2009-10-17 12:19:26 configure backuppc 3.1.0-4ubuntu1.1 3.1.0-4ubuntu1.1
2009-10-17 12:19:26 status half-configured backuppc 3.1.0-4ubuntu1.1

and apt/term.log:

Selecting previously deselected package exuberant-ctags.
(Reading database ... 398778 files and directories currently installed.)
Unpacking exuberant-ctags (from .../exuberant-ctags_1%3a5.7-4_i386.deb) ...
Processing triggers for man-db ...
Setting up backuppc (3.1.0-4ubuntu1.1) ...
Module cgi already enabled
 * Starting backuppc...
2009-10-17 12:19:22 Can't create a test hardlink between a file in /var/lib/backuppc/pc and /var/lib/backuppc/cpool. Either these are different file systems, or this file system doesn't support hardlinks, or these directories don't exist, or there is a permissions problem, or the file system is out of inodes or full. Use df, df -i, and ls -ld to check each of these possibilities. Quitting...
invoke-rc.d: initscript backuppc, action "start" failed.
dpkg: error processing backuppc (--configure):
 subprocess post-installation script returned error exit status 1
Setting up exuberant-ctags (1:5.7-4) ...

Processing triggers for menu ...
Errors were encountered while processing:
 backuppc

$ df -i /var/lib/backuppc/pc
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/sda3 14934016 955930 13978086 7% /
$ df -i /var/lib/backuppc/cpool
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/sda3 14934016 955930 13978086 7% /
$ df /var/lib/backuppc/pc
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda3 237044416 213036224 12061860 95% /
$ df /var/lib/backuppc/cpool
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda3 237044416 213036224 12061860 95% /

Relevant mounts (note that /dev/sdc1 is my external drive, and /dev/sda3 is my main disk):
/dev/sda3 on / type ext3 (rw,relatime,errors=remount-ro)
/dev/sdc1 on /media/backup type jfs (rw)