Because you are using a repack, some script signatures differ from the Steam version. Navigate to DayZ\Storage\_<yourname>\ and delete the missionsave folder. Also, ensure BattlEye is disabled in the launcher parameters.
For the Fitgirl Repack (which typically utilizes the or @DayZSP launchers), several mission files are highly compatible: Because you are using a repack, some script
mission files (like "DayZ SP" or "DaiZy") and drop them into the 3. Recommended Single-Player Mods Because you are using a repack