Can't insert cart using CI Cart Class

[eluser]ronaldlayanto[/eluser]
Hi, first of all, I'm a newbie at CI
Recently I develop a project which is require Cart class

I follow all the instruction in user guide, but still I can't add any single item into the cart
I loaded the library, I use the method properly, and for additional info I already set the config file to save the sessions into database

FYI, I use CI 2.1.2

Anyone has encountered this problem before?
Any helps will be appreciated

Thanks before