What you are seeing is a result of your long and or short positions being worth 0 (zero) in the calculation. For some reason the program they are using to capture delayed stock prices has some intermittent issues, and there are some bugs they need to work out. The negative number is the equivalent of all of your stocks crashing at once, and you being left holding your short stock promissary note, and your cash loan (remember you start with 100,000 and can borrow another 100,000). I am -28,000 because I borrowed -40,000 and borrowed 12,000 worth of short stock which has a positive value because it is borrowed stock at a certain price (it only becomes negative if you cover). Clear as mud?