Add-on shows error but works in tutorials

[nicki.t (nicki)]

Hello,
I am using blender 2.81a and I downloaded the Rigidbody addon from this tutorial:

- YouTube

But when I try to do use it it shows me this error:

But it should actually work with Blender 2.8. I tried it with other characters, repaired Blender 2.81 and much more, but I am doing the exact same things in the tutorial but it will always show me this error. How can I fix that ?

[irelevant (Frantisek Pastorek)]

I am not sure and sorry, if I am wrong. But have you installed python?

[nicki.t (nicki)]

I think I installed it a long time ago, I don’t really know. Could this be the reason for the error ?