Nível 3 Treinamento avançado - O projeto já tem uma referência ao Assembly

Good night,

I am in training and find myself in Level 3 Practice Lesson 1. I have been following the directions from the RPA channel video lesson on youtuber, I have used the REFramework made available in the environment itself. That said, when trying to create this variable, the message occurs: “The project already has a reference to Assembly”, I tried to create the variable tb in the menu below, but the same error appears. Accept any guidance or something that might generate reflection.

The tutorial I have been following is this:
https://www.youtube.com/watch?v=Y8MmF-61vqY The point in question is at 15:00

Following is the screen with the image where the error occurs: