WHMCS Permission Error

Hello,
Whenever I am trying to modify location of the writable folders in WHMCS setup I am getting permission error, though the permission is set to 777 but WHMCS could not load the folders. Forcing it to keep inside public_html only.

Also cron jobs not working for WHMCS. Please let me know what can I do to fix the issue? I have tried all but nothing works.