: Corrupted or incompatible settings saved in the .ini files.
Before we dive into fixes, it helps to understand why the error occurs. The "Cannot set display mode" error essentially means that the Serious Sam 3 engine (a modified version of the Serious Engine 3.5) is trying to request a screen resolution, refresh rate, or color depth from your graphics card that your monitor or GPU cannot deliver. serious sam 3 cannot set display mode