When there are two natives on one tile the right-click menu shows a "Activate all units" option (it shouldn't). Clicking this gives two pop-up messages "The Server cannot do that"; the log file on each message is the same
On the attached saved game, the native can be used to reproduce the error. I also attach the save game from before this turn and the log file. To get to the first save game position move the ship east until it finds the land, unload the Pioneer to the SE, then unload the Soldier to the South
Oh! - can't edit the post above
Save game "Bug2731.fsg" gives the error, save game "Bug2731lastturn.fsg" is the previous turn and "Bug2731.log" is the log file
Good catch, should be fixed in git.56f9fb9.