How to resolve 403 forbidden error

Hello community, I 've been experiencing this permissions error on discussion/forum and ads modules for about a month since resorting my site backup files. Something seems to have altered the default files and folders permissions.

I recently changed all files to 644 and folders to 755 but the error won't stop. It is more rampant with the admin account. I can't even upload profile photo or submit ad listings without experiencing the error. Please if there's a way to restore default permissions, I'll appreciate it. Thanks