"Roto Brush and Refine Edge is frozen. Unfreeze to update." Error pops up. More details inside

I am following a youtube tutorial to edit a video clip. I have rotoscoped a few frames, and when I click "Freeze", the computer does the work but then the error that is in the title pops up in a purple box. It won't let me freeze it, I tried unfreezing and redoing the process several times and it does not work. Crazy GHOST CLONE EFFECT ! (Adobe After Effects Tutorial) - YouTube I am up to 6:39 in this tutorial. Please help me, it is urgent! Any help would be greatly appreciated.