It is against regulatory rules to trade with your own orders. If you currently have a limit order working and you place a MKT order for the same product on the other side of the market, you will receive this warning as it is possible those two orders could trade with one another. To avoid this, use limit orders with specified prices so your open Buy and Sell orders will not cross.
Why did I get a warning message stating "Market Order was Repriced"?
A Cash account must have enough cash to cover the cost of a position plus commissions and can never hold a negative cash balance. When placing a Market order (or Stop order), the order value cannot be known with certainty prior to execution as the market can move in any direction at any moment. Because of this, an extra 5% is added to the order amount at the credit check step for Market type orders to account for market movements. If you receive an order rejection for not enough Settled Cash when you do in fact have the Settled Cash to execute your order at your desired price and quantity, try using a Limit order (or Stop Limit order for a Stop) or reduce the MKT order size…
The option market makers are allowed to post a Bid of "zero" as part of their two sided bid/ask market. If there is no bid for your long option you will not be able to sell it. Also a sell MKT market order can not trade when there is no displayed Bid. You can wait for a bid to appear and place a Limit order or you may have to hold the position until it expires and is removed from your account after expiration. …
Any size stock order, even if it is not in a round lot increments, can be submitted using a MOO, LOO, MOC or LOC order type. When you SMART route an At-the-Opening or At-the-Close order type, it will be routed to that symbol's primary listing exchange and given to the Specialist. There is never a guarantee that the Specialist will have enough shares available to match all the Buy and Sell orders they receive for an opening or closing cross. Orders are filled on a priority basis with the earliest submitted Market-on-Open orders filled first. If there are any shares still available to cross, the marketable Limit-on-Open orders with the earliest time stamps are next in line. If your order did not get filled, then there were not enough shares available for all of the orders submitted for the Opening or Closing cross trade…
The BATS exchange cut off time is 15:55 EST to submit a Market-on-Close (MOC) or a Limit-on-Close (LOC) order for consideration to be included in the closing cross. MOC or LOC orders submitted after 15:55 EST can be rejected, and you would receive a message stating "On-close orders cannot be placed during or near the closing cross"…