unserialize() error – secure.php on line 20

When I try to hit the “Create Backup Button” or the “No, already have a backup” button I get this error:

Notice: unserialize() [function.unserialize]: Error at offset 0 of 76 bytes in /home/user/public_html/launchblog/stageblog/wp-content/plugins/better-wp-security/inc/secure.php on line 20

What does it mean?

http://wordpress.org/extend/plugins/better-wp-security/