Probleme with square render texture

Hello
I’am new, i use blender since 1 month.
Actually i have a work for a client for modeling a short animation.
All is ok except when i make movie, i have some square that apear and displace on my grass texture
D’ont know why i have this render, if somebody can take a look and explain me

There is the link to show my problem
https://vimeo.com/118328977

Link “page not found”