I have been trading with IB for nearly twenty years and use the classic TWS, and when I was trying to put a futures stop order in late this afternoon (before 4:14 EST), I could not place the order. Instead, I received the following message: the "display size" order attribute may not be specified for this order. I could not find the message in the long index of message codes. I have tried to configure the order attributes section. Nothing seems to work. I am not trying to put in a complicated order: merely a buy stop order slightly above the market No conditions. I don't even have the "display size" on my quote screen. What should I do? Thank you.