If you receive a message stating "This server is running a modified version" try these steps.

Unsubscribe. Wait 10 - 20 seconds then subscribe again.

If that doesn't work then:
Unsubscribe. Locate your steamapps folder then workshop>content>304930>you will see a lot of folders. Sort by "most recent" by clicking "Date modified". The top folder will have the most recent date. Locate my map's folder by opening the top folder(s) until you see another folder inside with the name "The Final Days II". Delete the folder that contains my map (if the folder with my map in it can't be found then it was already removed when you unsubscribed). Now go back to steam and resubscribe.

This also works for other workshop mods.