I dont know if this will fix your problem but it is worth a try
Step 1: Log out of steam and close the application comepletely (Task Manager after loggin out)
Step 2: Go to your steam folder in your program filee
Step 3: Search in the steam folder for a folder labeled "appcache"
Step 4: Delete the folder labeled as "appcache"
Step 5: Restart steam and log in the boot your game and see if the problem is solved
IDK if iut will fix this problem but I know it is working for the people wiht the new DLC getting the Invalid map file errors