Plugin not working because of database issues

Hi, after I tried to save my settings on the settings page, I received some database error messages, see below (XXXX are the hidden directory path)

Warning: mysql_real_escape_string(): Access denied for user ‘root’@’localhost’ (using password: NO) in /XXXXXXXX/wp-content/plugins/hide-real-download-path/hide-download-path.php on line 74

Warning: mysql_real_escape_string(): A link to the server could not be established in /XXXXXXXX/wp-content/plugins/hide-real-download-path/hide-download-path.php on line 74

While it seems I was still able to manage to save the Base dir setting, it seems the plugin is not working.
– when I try to insert Allowed referral and try to save, it says “Something went wrong while saving data, please try again.” It does not save.
– I can successfully create the download page and insert code, but when I try to download the selected file the right way (http://YourSiteName.com/YourPageName/?f=YourFileName.extension) I get the following error message:

Warning: readdir() expects parameter 1 to be resource, boolean given in /USER/dayone/dayonecapital_com/www/wp-content/plugins/hide-real-download-path/hide-download-path.php on line 379
File does not exist. Make sure you specified correct file name.

What can be wrong?

https://ww.wp.xz.cn/plugins/hide-real-download-path/