UE4 crash when building light ?

before one month un4 work great.
now , every time i use : build or (build lighting only), new or old project , new or old level

I have this message

https://img15.hostingpics.net/pics/186561Sanstitre.jpg

and the un4 crash and dosn’t work at all.

what kind of setting i must change it ?

Thank’s