Metaquotes introduced a new method for describing the market environments and this requires an active connection to a broker even when using the Strategy Tester and backtesting on historical data.
At the moment it is unclear if this is a bug or a feature that will remain in the code code in the future.
What this means for users of SphereTester:
If you are trying to run a backtest without being connected to a broker opening orders will result in a 131 Ordersend Error and no position will be opened.
To resolve the issue simply make sure that you have an active connection to your broker by logging in to your account and/or connecting to the internet. The connection status indicator can be found in the bottom right corner of the MT4 window, if the status bar is green then an active connection is present, if it is red then there is no active connection.