The spice model associated with the Ammeter symbol had been accidentally removed from the spice model library. The model has now been replaced but the Ammeter symbol has also had to be modified. Simulation schematics with the old Ammeter symbol may no longer work. If you encounter this problem, please delete the Ammeter symbol from your schematic, do a SHIFT+F search for Ammeter then select the one with a small blue "S" in the icon on the left of the search results:  and then replace the ammeter instances in your schematic with the new symbol. Sorry for the inconvenience.