Fatal Error : job_start.php on line 20

Fatal error: Temporary directory unavailable in wp-content/plugins/backwpup/job/job_start.php on line 20

I don’t understand why it says that when I start the backup.

By the way, there are three errors too when I activated the plugin :

- The temporary directory
wp-content/plugins/backwpup/tmp/ doesn't exist !
- The temporary directory
wp-content/plugins/backwpup/tmp/ is not writable !
- The directory of log files
wp-content/backwpup-98372-logs/ doesn't exist !
- The directory of log files
wp-content/backwpup-98372-logs/ is not writable !

Please help me, sorry for my bad english, i’m french.

Regards

http://wordpress.org/extend/plugins/backwpup/