Error: trying to add tablespace

I recently performed a mysqldump and restore of a large dataset as some tables were not using individual tablespaces. After this completed, the following day I experienced an error while performing a backup using xtrabackup (std backup managed through cron).

xtrabackup version 1.6.3 for Percona Server 5.1.55
MySQL version: 5.1.38

Error:

InnoDB Backup Utility v1.5.1-xtrabackup; Copyright 2003, 2009 Innobase Oy
and Percona Inc 2009-2011. All Rights Reserved.

This software is published under
the GNU GENERAL PUBLIC LICENSE Version 2, June 1991.

IMPORTANT: Please check that the backup run completes successfully.
At the end of a successful backup run innobackupex-1.5.1
prints "completed OK!".

innobackupex-1.5.1: Using mysql Ver 14.14 Distrib 5.1.38, for unknown-linux-gnu (x86_64) using readline 5.1
innobackupex-1.5.1: Using mysql server version Copyright 2000-2008 MySQL AB, 2008 Sun Microsystems, Inc.

innobackupex-1.5.1: Created backup directory /mnt/hot_backup/new
111207 11:04:06 innobackupex-1.5.1: Starting mysql with options: --defaults-file='/etc/my.cnf' --password='xxxx' --unbuffered --
111207 11:04:06 innobackupex-1.5.1: Connected to database with mysql child process (pid=1449)
111207 11:04:11 innobackupex-1.5.1: Connection to database server closed

xtrabackup: uses posix_fadvise().
xtrabackup: cd to /data/database/db_data
xtrabackup: Target instance is assumed as followings.
xtrabackup: innodb_data_home_dir = /data/database/db_data
xtrabackup: innodb_data_file_path = ibdata1:2000M:autoextend
xtrabackup: innodb_log_group_home_dir = /data/database/db_data
xtrabackup: innodb_log_files_in_group = 3
xtrabackup: innodb_log_file_size = 157286400
xtrabackup: use O_DIRECT
111207 11:04:11 InnoDB: Warning: allocated tablespace 24, old maximum was 9
InnoDB: Error: trying to add tablespace 8 of name './database/table1.ibd'
InnoDB: to the tablespace memory cache, but tablespace
InnoDB: 8 of name './mysql/inventory.ibd' already exists in the tablespace
InnoDB: memory cache!
innobackupex-1.5.1: Error: ibbackup child process has died at /usr/bin/innobackupex-1.5.1 line 336.

I was not able to find any related posts and Google searched yielded no results. Any feedback is appreciated.

Thanks.