Seem to be doing somthing wrong throws an error.

            foreach (var AtmID1 in npcData.Atm.Values)
             {
            var networkable = BaseNetworkable.serverEntities.Find(Convert.ToUInt32(AtmID1.AtmID));
            var entity = networkable as BaseEntity;
            if(entity == null) {
            Puts("Remvoing from config Atm not Found ID" + Convert.ToString(AtmID1.AtmID));
            npcData.Atm.Remove(AtmID1.AtmID);​

Dop i forgot the return;
i got it

Consider using and IDE with static code analysis tool. Fast and free tool - VS Code with OmniSharp extension.