Factorio 0.17.35 (build 44769, win64, steam)

Error MainLoop.cpp:1173: Exception at tick 6276: The mod GhostPlacerExpress caused a non-recoverable error.
Please report this error to the mod author.

Error while running event GhostPlacerExpress::on_selected_entity_changed (ID 52)
real number expected got nil.
stack traceback:
GhostPlacerExpress/control.lua:66: in function <GhostPlacerExpress/control.lua:53>
stack traceback:
[C]: in function 'get_inventory'
GhostPlacerExpress/control.lua:66: in function <GhostPlacerExpress/control.lua:53>

The new update (0.17.35) has changed player to character in the api.

For this mod, in Control.lua line 66, replace the line with the following:
local player_main_inventory = player.get_inventory(defines.inventory.character_main)

The change is player_main to character_main

Thank you for the report and thanks for the update-- updated with the change.