I get this error semi-randomly when interacting with the fuel slots in a locomotive, seems to happen every time when placing the cube into a fuel slot.

Error while running event Ultracube::on_tick (ID 0)
Ultracube/scripts/cube_search.lua:153: attempt to index local 'inventory' (a nil value)
stack traceback:
Ultracube/scripts/cube_search.lua:153: in function 'check_inventory'
Ultracube/scripts/cube_search.lua:250: in function 'cube_check_entity'
Ultracube/scripts/cube_search.lua:560: in function 'cube_search_graph'
Ultracube/scripts/cube_search.lua:846: in function 'update'
Ultracube/scripts/cube_fx.lua:286: in function 'tick'
Ultracube/control.lua:262: in function <Ultracube/control.lua:261>

Thanks, will fix when I get a chance. For now probably just avoid putting the cube in that slot (there's another way to use the cube with trains that should work fine once you get the right tech).

This exact bug occurs with trains even when not handling fuel or using the cube in them , could be caused by a train merely consuming condensed fuel.
It could be very problematic as it prevents using trains altogether. EDIT : was with version 0.2.2

I think it should be fixed now with the patch that was released earlier, please let me know if you do see any more problems.

So far so good with version 0.2.4 , haven't crashed in a few hours with trains driving around.