Codemasters games (DiRT 2, DiRT 3, GRID, GRID 2, F1 2010, F1 2011, F1 2012, F1 2013, etc.) use UDP network and requires special permission in Windows 8 and 8.1 to communicate with other applications like SLIMax Manager.
if Codemasters games not working on your Windows installation start by running SLIMax Manager as Administrator to avoid any permission issue.
This is applicable to Windows 8, Windows 8.1 and Windows 10, to solve your permission issue run the app as administrator :
see How to run app as administrator
How to configure the Codemasters game, FAQ