No achievements or challenges. 'No user modifications that change the game's checksum'

[Einar Stormcrow]

I just redownloaded the game, and wanted to do the challenges as that was something new for me. Unfortunately, every time I try, I am unable to start a game. On the list of requirements, the one it is telling me I do not meet is 'no user modifications that change the game's checksum'. On occasion it will say that I'm 'not connected to Steam' before the error again changes to the modification/checksum message. The thing is, Steam is running, and I've only just downloaded the game again. There are no mods. When I played the game last, I used no mods. I am currently subscribed to no mods on the Steam Workshop (I double checked). I have uninstalled and reinstalled the game again. I've gone into documents/paradox, found what CK2 files were left and manually deleted them before reinstalling. I have tried both unsynced and synced to the Steam cloud. I have disabled both the Customization Pack and ruler designer DLCs. The problem persists, and I'm at a loss. Has anyone else run into this? What am I missing?

 

[ThatGuyFromSeinfeld]

Manually delete the files in the Documents folder and the actual game files and then Verify Game Files in Steam