add_filter does not work as expected

Your plugin code is going to run before the theme code and hence will run before anything is added to the hook. You will need to the code that processes the file inclusion to some other hook that runs after all of the plugins load, like after_setup_theme

This should help: Is there a flowchart for wordpress loading sequence?

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