If you get this message when opening the SDK or Red Orchestra 2 then I have found a possible solution. FOLLOW INSTRUCTIONS CAREFULLY.
- Exit Steam
- Find steam folder. Usually it is here: Program Files (x86)\Steam
- Move/Cut the steamapps folder and save it somewhere else and rename it steamapps_backup THIS IS SUPER IMPORANT! This is where your games are.
- Uninstall Steam
- Re-install steam
- Rename steamapps_backup to steamapps and overwrite the existing steamapps inside the Steam folder.
- Open Steam