1) Before you start
- Remember that the game uses certain ports
- Setup or turn off your security software (antivirus, brandmauer, UAC, SmartScreen, etc.)
- Make sure that you're logged into Windows as Administrator
- Open context menu by a right click on game's icon, go to Compatibility settings and choose to Run as Administrator
Also, before installing the game you might want to read these helpful articles by Microsoft customer support:
Note: if you decide to do a clean launch, please, be considerate and careful. Do not modify any services that you're are not familiar with. Details about running services may be found in the Task Manager or in Control Panel -> Administration -> Services. You may also use the standard Backup features offered by Windows.
Normally these recommendations are enough for the launcher to work properly. All that is said is applicable to a correctly intalled game with it's installer downloaded from the profile.
In case if none of these recommendations helps, please, re-install the game and place it into a folder with shorter path, for instance, "C:\Games\IL-2 Sturmovik Battle of Stalingrad".