Rotobrush not working very well

I have a problem everytime I use the  Rotobrush tool and I still don't know how to solve it.

I finished rotoscoping the first frame of my video but when I try to move to the next frame or play the video to see if it holds, the clip freezes and then, when I come back to the composition, everything turns black and and on the layer window, it says that it's installing a propagation module of Rotobrush. I wait but nothing happens.

At first, I thought it was because of my first clip. So, I changed it with another video with a lower resolution but it's the same problem. I use 8 Gb computer and I don't know if it is because of that I can't use the rotobrush tool correctly.

I even deleted the cache files and made a few modifications, but nothing helped.

I'm starting to think I need to buy a better PC but if there's a solution to this problem please, let me know ! It would be grateful.