Sometimes Sim4Life does not work after I reboot my computer: it says the license is invalid...

This could sometimes happen if the license server is located on the same machine where Sim4Life is running. If the machine is rebooted and Sim4Life somehow starts before the license server is up and running, it can lead to some strange behavior.

The license server is installed as background Windows Service which start automatically after system reboot, with a few minutes delay. This delay is recommended by Microsoft in order for third-party services not to interfere with system services. Therefore, the usual approach is to wait a few minutes before launching Sim4Life. In some cases, if you tried to point the licensing file again, you might corrupt the license server (but this rarely happens as there are a few safeguards in place).

The best way to fix the issue now is to run the tool "Install License" again and reinstall the license as initially instructed. After that you should be able to use Sim4Life normally after system reboot, as long as you wait 3-5 minutes before starting Sim4Life.