This message indicates that an error occurred while attempting to plan the trade. The trade planning process was not successfully completed, which means the trade could not be executed.
When TradersPost executes a trade, the first thing it does is communicate with the broker to fetch the state of the broker account. This includes fetching current open positions, open orders, account balances, and any other information required to execute the trade. TradersPost then uses this information to determine the trade plan, which includes deciding whether to cancel any open orders for the ticker, exit the open position if it exists, or enter a new position. If there were any problems communicating with the broker or processing the trade plan, you will see this message.
You can turn on retries within TradersPost for these kinds of failures. In your strategy settings, scroll down to the Retry section and check the Retry trades that fail during trade planning checkbox.