Advanced Password Hash could not be activated because core files could not be modified. Please check the documentation CHMOD permissions and try again.

[xSynthx]

I tried installing this plugin, and I got this error :/
And these are my chmod settings, they are all correct

[JordanMussi]

inc/functions_user.php must be writable for the core edits to be successful.

You can perform them manually as well:
Find the line starting with:

function validate_password_from_uid

Replace the whole line with:

require_once MYBB_ROOT.'inc/plugins/psswrdhsh/functions_user.php';
function old_validate_password_from_uid($uid, $password, $user = array())