Cannot start xtrabackup

I hope someone can help, I have been working on this for two days with no luck.
The OS user which runs the database is the same user I start Xtrabackup as. The OS user has complete ownership of the MySQL directory, the Xtrabackup directory and my backup destination directory. When I start Xtrabackup it fails with the error below. Any ideas. Thanks

InnoDB Backup Utility v1.5.1-xtrabackup; Copyright 2003, 2009
Innobase Oyand Percona Ireland Ltd 2009-2012. All Rights Reserved.

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

IMPORTANT: Please check that the apply-log run completes successfully.
At the end of a successful apply-log run innobackupex
prints “completed OK!”.

130315 13:54:42 innobackupex: Starting ibbackup with command: /opt/percona/percona-xtrabackup-2.0.5/bin/xtrabackup_55 --defaults-file=“/opt/mysql/mysqldb/db/db.cnf” --defaults-group=“mysqld” --prepare --target-dir=/opt/mysql/database_backup

/opt/percona/percona-xtrabackup-2.0.5/bin/xtrabackup_55 version 2.0.5 for Percona Server 5.5.16 Linux (x86_64) (revision id: undefined)
xtrabackup: cd to /opt/mysql/database_backup
xtrabackup: Error: cannot open ./xtrabackup_checkpoints
xtrabackup: error: xtrabackup_read_metadata()
xtrabackup: This target seems not to have correct metadata…
130315 13:54:42 InnoDB: Operating system error number 2 in a file operation.
InnoDB: The error means the system cannot find the path specified.
xtrabackup: Warning: cannot open ./xtrabackup_logfile. will try to find.
130315 13:54:42 InnoDB: Operating system error number 2 in a file operation.
InnoDB: The error means the system cannot find the path specified.
xtrabackup: Fatal error: cannot find ./xtrabackup_logfile.
xtrabackup: Error: xtrabackup_init_temp_log() failed.
innobackupex: Error:
innobackupex: ibbackup failed at /opt/percona/percona-xtrabackup-2.0.5/bin/innobackupex line 381.

try this:

cd /opt/mysql/database_backup
touch test

and see whether you can create the file.

Yup I can create the file. In fact I created xtrabackup_checkpoints & xtrabackup_logfile files manually and tried to run the following command and received the below error.

innobackupex --user=root–password=password–defaults file=/opt/mysql/mysqldb/db/db.cnf /opt/mysql/database_backup --no-lock --apply-log – ibbackup=xtrabackup_55

xtrabackup_55 version 2.0.5 for Percona Server 5.5.16 Linux (x86_64)
(revision id: undefined)
xtrabackup: cd to /opt/mysql/database_backup
xtrabackup: error: xtrabackup_read_metadata()
xtrabackup: This target seems not to have correct metadata…
InnoDB: Error: tried to read 2048 bytes at offset 0 0.
InnoDB: Was only able to read 0.
130316 9:32:22 InnoDB: Operating system error number 0 in a file
operation.
InnoDB: Error number 0 means ‘Success’.
InnoDB: Some operating system error numbers are described at
InnoDB: File operation call: ‘read’.
InnoDB: Cannot continue operation.
innobackupex: Error:
innobackupex: ibbackup failed at /opt/percona/percona-xtrabackup-2.0.5/
bin/innobackupex line 381.