Could it be that the stocks are on the NYSE RegSho list? I've noticed that if they are on the list, IB won't allow you to short them. I had that issue w/ SPWR and LTM
I'm only trading nasdaq & amex. Do they have a similar list? One stock I wanted to short went down 10% yesterday. So I'm wondering why they're not shortable? Not all do that, some go up. I imagine they go up easily if no one can short them. But the one that dropped 10% would have been nice.