I tried to linearise the plant in the model you attached, but I didn't find the error you described. I linearised the PWM generator as an example block, and generated a Bode Response. I've attached it below for your reference if necessary.
You can refer to the instructions detailed here, Linearize Plant Using Model Linearizer, for details on using the Model Lineariser. You can also linearize a plant subsystem at Command Line in a Simulink model using thelinearizecommand.
If you are still continuing to face an error, a more detailed description of the steps you took and the errors would be helpful.