Hey suan2,

I get this error whenever I load a game (works just fine until a game is loaded):

The mod Utilization Monitor (0.6.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event UtilizationMonitor::on_tick (ID 0)
UtilizationMonitor/control.lua:251: attempt to call field 'is_working' (a nil value)
stack traceback:
UtilizationMonitor/control.lua:251: in function 'update_entity'
UtilizationMonitor/control.lua:458: in function <UtilizationMonitor/control.lua:424>

Note that I can disable the mod, restart Factorio, enable mod again and load and then it works just fine, but I cannot load a game as is.