The problem doesn't obviously have anything to do with GSX but, as the message clearly says, it's caused by another program blocking the installation of the .dll module required by GSX to start, which is most likely the same issue which is causing any problems in the sim.
The most common case is a defective antivirus, which has mistakenly blocked the installer from copying the file, so you must:
- Restart Windows
- Disable the antivirus
- Reinstall
- Configure the antivirus to exclude the sim folder from scanning.