Scottrade did exactly the same thing to me. They let me go on margin in ultra 3x ETFs and without warning totally made them unmarginable and gave me a large margin call forcing me to sell my positions and scaring the hell out of me about the safety of the the stocks. They refused to give an explanation of why they went from 65% to 0% marginability. I sold out my positions that I had gone into expecting a large move in the market and the next day the move happened costing me a huge amount of money because I missed it. I am contacting a securities attorney and expect to be filing suit. Would anyone like to join me?