There is an unnecessary ~= nil in there.

Line 88 of BuildableRoads_UI_Button.lua should be:

if bIsUnitSelected and (iLocationX~= nil and iLocationY~=nil) then

@DARKNESS, Thanks for the report! I think I know the Issue, will try to fix it tomorrow.

Thanks for the mod. Unfortunately log is flooding with this runtime error:

Runtime Error: C:\Games\Steam\steamapps\workshop\content\289070\3099167580\BuildableRoads_UI_Button.lua:88: attempt to index a nil value
stack traceback:
C:\Games\Steam\steamapps\workshop\content\289070\3099167580\BuildableRoads_UI_Button.lua:88: in function 'BuildableRoad_OnUnitSelectionChanged'
C:\Games\Steam\steamapps\workshop\content\289070\3099167580\BuildableRoads_UI_Button.lua:69: in function 'BuildableRoad_OnUnitMoved'
[C]: in function 'func'
[C]: in function '(anonymous)'