I have been very happy with IB for many years - never had a problem, and great options executions and commissions. For example, last week, sold 20 SPY calls as part of a vertical credit spread, for 30 cents each commission. Often I can buy at bid and sell at ask, even when price doesn't trade through my level. But today was a real wake up call. I tried to close some SPY OCT call credit spreads for a loss, and TWS would not let me, saying that it would increase my margin deficit. This didn't make sense for 2 reasons - by closing the position, I would be REDUCING my margin requirement, and I knew I was nowhere near my margin limit. I called IB at 12PM, and within 2 minutes I was speaking with a rep. He spent 15 minutes with me, very friendly, but he explained there was nothing they could do. Turns out TWS has this weird way of calculating margin sometimes. I only do credit spreads on SPY, so at all times the number of short calls always equals the number of long calls. But TWS used some NOV long calls to offset some OCT short calls, such that I ended up with TWS treating 20 NOV short calls as naked! The 20 OCT long calls that were bought to offset the OCT short calls were not offsetting anything. So I had to do a lot of trades today to eliminate this situation, that I would never have done. Anyone else have this problem?