Are you loading the game up with no mods? Because any mod will change the checksum.
If so, you'll need to do a full clean reinstall:
If this is Steam: uninstall the game from Steam and move any valued save games elsewhere. Manually delete ALL the CK2-related files and directories from under the Steam AND MyDocuments folders, now reinstall the game via Steam. Now run the Steam client option to Verify Game Cache Files until it runs clean.
If GamersGate: Move valued save games elsewhere, and uninstall the game. Manually delete the CK2 directories from where GG put them and from MyDocuments. Reinstall the game , download 1.092 patch again and apply it.