/%post_name%/ or /%postname%/ in Permalinks?

/%postname%/ is the correct one and if you are asking be cause it says post_name in the codex then its just to show that you will get the actual post name.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)