You do not have sufficient permissions to access this page error while accessing theme-editor.php

I am doing 1 project which uses both language.
There was not session.php file so i downloaded wordpress 4.2.2 respective of my project and put that file in includes file and the website works fine but when i try to post i am not able to write anything.
What is the problem i don’t know.
While accessing theme-editor.php, it shows You do not have sufficient permissions to access this page error