There is probably a stale .lock file in the settings folder. Delete it manually and try to launch Studio again.
You can find the Studio settings in the following locations:
- Windows:
C:\Users\USERNAME\AppData\Roaming\GAMS\ - MacOS & Linux:
$HOME/.config/GAMS/
Sometimes this occurs on systems with multiple graphics cards. Try to run GAMS Studio with a specific graphics card to solve the issue.