NinjaTrader 7 and NinjaTrader 8 suffer from time to time from stuck pending orders or suck orders pending cancel
How to remove stuck pending orders?
This is the reply from NinjaTrader
Reset your SIM 101 account. Resetting a simulation account will clear all historical trade data from this account. Please follow the instructions below to reset a simulation account (this can take longer depending on the size of your database file and your system):
- From the NinjaTrader Control Center window select the menu Tools> Options> Simulator.
- Press the 'Reset' button.
- If you do not want to lose your trade data, uncheck the 'Clear history' box (This must be left checked when wanting to remove a stuck sim order)