The heart of Proteus has always been ISIS (Intelligent Schematic Input System). Version 9.1 brought:
Solution: Run Library Manager > Rebuild again. If still missing, manually copy the updated .LIB files from the update’s LIBRARY folder into the installation directory. proteus 91 full upd
Routing complex boards in older versions of Proteus was often tedious. The updated routing engine includes: The heart of Proteus has always been ISIS