Issue: Cannot start Singleplayer game
There are 3 most likely possible reasons why you cannot start singleplayer game.
Your firewall is blocking internet access to VoidExpanse (local server). VoidExpanse, even in singleplayer mode uses networking to connect to a server (which in this case is running on your computer).
Antivirus blocking application
Your antivirus is blocking VoidExpanse application. The best option to solve this issue would be to add VoidExpanse to your antivirus exclusions.
Antivirus removing some critical files
Some people reported that some critical files, such as server executables were removed by their antivirus. You have to add these files or the whole folder into exclusions and the game would work.
Antivirus blocking creation of child process
Singleplayer mode works with a local server running on your computer silently, in invisible mode. This requires permission for VoidExpanse to start a child process. Your antivirus may be blocking it. The best option to solve this issue would be to add VoidExpanse to your antivirus exclusions.