Has this always happened ever since you've had the game, or only since what change or update?
Does it always happen in every game, every part of the map, or what?
DXDIAG is a program you run from a command prompt or the Windows start menu 'run' dialog box (or 'search programs' in Windows 7 or later). After running it will open a window and start collecting info with a progress bar in the lower-left corner. When it completes click the 'save all information' button and save it to a file then attach that file here.
Please attach your Documents/Paradox/Imperator/pdx_settings.txt.
From your Documents/Paradox/Imperator/logs/ folder, attach system.log .