I fixed the problem.
After trying many ways to solve the problem, i tried this one and fixed it.
First i deleted the DDC and ZEN folder in
C:\user%username%\appdata\local\unrealengine .
I had some assets and directional light and etc in my default level ( the level which opens in my project stratup), so i delete all of’em in the default level.
Then i entered to my problematic level and tried to render again and this time every thing was alright.