Eragon nds - please help me!

I played eragon game for nds in my pc and I'm confused.. Why can't I collect any herb? Our maximum quantity for the herbs or 3 right? But even my number of herb is 1, I sometimes can't collect it.. And sometimes I can. And when I collect it, the number of my herb didn't increase.. I'm so confused because of it.. What should I do? Thank you..

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