This error usually happens because the game cannot connect to the authentication server to verify your ownership, or the local license file has become corrupted. This is common with older software like ATC4, especially if the original publisher has changed servers or if you have changed hardware on your PC.
Windows Defender or other security software can block the application from accessing essential save data folders. Windows Defender or other security software can block
, it can cause pathing errors where the executable cannot find its configuration or save files. Right-click the ATC4 shortcut or
ATC4 can be picky about Windows user permissions, especially when trying to write temporary verification files. Right-click the ATC4 shortcut or .exe. Select Properties > Compatibility. Check Run this program as an administrator. Windows Defender or other security software can block