Artisan Archive

I just picked up Business III so i could create a vendor to sell my harvested resources, and some traps and camps.

i setup the vendor, and tried to add stuff to it, and it wouldnt let me. it tells me "You cannot sell and invalid item". well i finally was able to add 1 (its a sonic pulse trap), but when i try to sell another one, it gives me the same "You cannot sell and invalid item" message. so i try a different item, and SAME MESSAGE!
Please help, as you can imagine this is VERY frustrating.

Second question, how do i add items to my stockroom, and what is the stockroom really for?

thanks for your help, im just starting out as an artisan and would really like to figure this out so i can keep crafting. =)