Can't buy items from FM

So I am having trouble buying some items from FM.
Everytime i try to buy a scar helm form anyone in fm I can't and it keep saying that my inventory is full.

Anyone else having this problem or any way to solve it?
I've tried channel changing and relogging but nothing ever works.

Thanks in advance for any help

Read what you type! Your Inventory is full. Drop some items, then it should work.

if it was that easy i wouldn't have to post here
i've tried this with nothing in my inventory before and still nothing

Maybie its because u already have a scar equiped?

so even if i unequip i can't buy? i have to like throw out my current one or something?