This is a common symptom of a version mismatch between the server and client.
It happend most probably due to an update with one of the sides still running an older version.

- Close your DayZ (and all launchers) and Steam completely!
- Restart Steam and watch it for DayZ Workshop updates.
- If it doesn't start updating by itself try starting DayZ through Steam,
- once started it should say "Some mods were recently updated" Imgur[imgur.com]
- Go to Mods and check that "Rostowmap" has a red updated next to its name, check the last update time to be recent.

should look like this[imgur.com]

- Repeat until updated


- update by copying the mission folder from the mod into mpmissions
- if you have customized your types or any other file they have to be merged. if you just overwrite them your changes will be gone, if you don't you won't have changes from the update.
- restart your server (!)