The mod Math combinator (1.1.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event MathCoProcessor::on_gui_click (ID 1)
MathCoProcessor/gui.lua:130: attempt to index field 'player' (a nil value)
stack traceback:
MathCoProcessor/gui.lua:130: in function <MathCoProcessor/gui.lua:129>

the current implementation relies on a player because in the dialog close event I have to know for which entity I opened the dialog and I cache this on the player index.
I debugged a "sandbox" mission and even then a player was found.
I don't know if this is new or I have started the game still in another way then you.
Can you provide me the click path form the main menu?