This error has been resolved as of version 1.3.0 for Landing Challenge Pro. Ensure you have the latest version installed.
We have very rare reports where sometimes a challenge is loaded and the aircraft doesn't have any fuel. Whilst we have worked to identify this bug and resolve it, no solution was found to fix this problem.
That said, there is a workaround for those very rare occasions it does happen.
Solution - Reload the mission from the activities menu
Close the Landing Challenge and head back to the main menu of the simulator. Select the same challenge again.
Should this continue to happen after trying the solution, please submit a support ticket. Please be descriptive and provide screenshots where possible.