The following two blocks cannot be connected in series because they are modeled as current sources:
Block 1: A_rotor: Asynchronous Machine SI Units
Block 2: B_rotor: Asynchronous Machine SI Units
Add a high-value resistance in parallel with one of the two block.
You can also specify high-value resistive snubbers if the blocks have a snubber device.You can also avoid the use of the snubbers by selecting the 'Enable use of ideal switching devices' option of powergui block.