When I edit the Contrast number at the bottom (0.6) I get the error attached at the bottom after attempting to play.
It’s a Post Processing component in a Third Person Character.
https://puu.sh/wfsXg/1af51c0ab9.png
https://puu.sh/wfsLP/6f8cd6e6f3.png
EDIT:
Appears to only do it upon typing a value rather than using the slider.