Hi, in the documentation section there is a list of the file permissions necessary for the cart to work correctly.
Here's the link to the doc pages (they are quite useful when learning about this cart)
http://www.abantecart.com/ecommerce-documentation/20-installation (http://www.abantecart.com/ecommerce-documentation/20-installation)
The files are
For Linux/Unix make sure the following folders and files are writable.
chmod 0777 system/config.php chmod 0777 system/ chmod 0777 system/cache/ chmod 0777 system/logs/ chmod 0777 image/ chmod 0777 image/thumbnails/ chmod 0777 download/ chmod 0777 extensions/ chmod 0777 admin/system/backup/
Check to see if you're permissions are set as suggested.