91.557 Error MainLoop.cpp:1202: Exception at tick 109511: The mod Cities Of Earth (0.3.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event CitiesOfEarth::on_gui_click (ID 1)
CitiesOfEarth/scripts/coe_gui.lua:7: attempt to index field 'parent' (a nil value)
stack traceback:
CitiesOfEarth/scripts/coe_gui.lua:7: in function 'OnGuiClick'
CitiesOfEarth/control.lua:20: in function <CitiesOfEarth/control.lua:20>
91.557 Error ServerMultiplayerManager.cpp:90: MultiplayerManager failed: "The mod Cities Of Earth (0.3.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event CitiesOfEarth::on_gui_click (ID 1)
CitiesOfEarth/scripts/coe_gui.lua:7: attempt to index field 'parent' (a nil value)
stack traceback:
CitiesOfEarth/scripts/coe_gui.lua:7: in function 'OnGuiClick'
CitiesOfEarth/control.lua:20: in function <CitiesOfEarth/control.lua:20>"

ouch! I'll look into that. Thanks for the detailed info.
What city were you trying to select?

it happened just when joining and two people were in new york and a third got into the lobby - might have spawned on Nauvis though.

was the 3rd player able to re-join?
I don't have the ability to test 3 player at the moment...

nope, had to remove this mod to allow them to spawn.

Please try this update - 0.3.3. I made a small change to the UI which should prevent the error you had.
Please let me know if it doesn't work.

there was a bit of other info i missed out on that when this player joined, we see a printed message to console that the game map settings have changed and there's no way to prevent it, but to revert them - before the server says Not Responding.

26.955 Error ServerMultiplayerManager.cpp:90: MultiplayerManager failed: "The mod Cities Of Earth (0.3.3) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event CitiesOfEarth::on_init()
Invalid surface name: Surface names must not be blank and must be unique.
stack traceback:
CitiesOfEarth/scripts/coe_setup.lua:152: in function 'MakeLobby'
CitiesOfEarth/control.lua:26: in function 'OnInit'
CitiesOfEarth/control.lua:19: in function <CitiesOfEarth/control.lua:19>
stack traceback:
[C]: in function 'create_surface'
CitiesOfEarth/scripts/coe_setup.lua:152: in function 'MakeLobby'
CitiesOfEarth/control.lua:26: in function 'OnInit'
CitiesOfEarth/control.lua:19: in function <CitiesOfEarth/control.lua:19>"

Is that message - "game map settings" - new for 0.3.3 or was it 0.3.2?
Also, that seems like his mod settings might be corrupted. Perhaps if he renames his mods folder and creates an empty one, it will clear up, because it will download them from the server.

So, MakeLobby creates a surface (named 'Lobby'), that is the default spawn area. That code didn't change, then there must be a conflict with the save file that it already has a surface named "Lobby". I will try renaming my lobby to "CoE_Lobby" to see if that resolves the issue for you.

0.3.2 did that.

the lobby surface came from CoE being here already once, maybe you can just recreate it? or check if it exists first?

That's a good idea - I'll add that now - hold off on 0.3.4.

I have published 0.3.5 which uses the lobby name of "CoE_Lobby" and checks that it doesn't exist before attempting to create it. However, it doesn't change an existing world, so if you are still getting that error, you might have to make a temporary change to your local copy to change the lobby name back to "Lobby" (it is in 'config.lua').
I'm not sure on how you are getting the errors, so I'm kinda guessing as to fixes.
I appreciate you working with me to make the mod better!

no problem, i think there's a bug in factorio right now with mod-settings.dat transfer as well that causes the mod settings error when they joined..