Comment 35 for bug 102097

Please check whether you have the package usbmount installed. Usbmount is a package that works with udev to automount usb devices. If you got it installed, then check /etc/usbmount/usbmount.conf to make sure it includes vfat filesystem. Usbmount's default configuration for filesystem support only includes ext2 and ext3.

http://joekuan.wordpress.com/2009/03/03/troubleshooting-on-usbmount/

Hope this helps