This error message means that something is preventing 3DMark from using exclusive full-screen mode in DirectX 12.
There are a few possible causes for this error:
- You have an overclocked display panel. If so, return the panel to its default settings.
- There is a problem with your graphics driver. Try removing then reinstalling the driver.
- There is a program blocking exclusive full screen mode. Close apps that draw overlays on the screen.