The issue is with folder permissions - at least, 95% of all cases like this are down to this.
Basically, whenever you create a folder on the server, you're giving it user-based permissions (NOT chmod). This is like a Windows user being able to create a folder on the desktop - they might not have permission to do it, so they get an error. The forum folders need to be writable for the PHP user setup on your server.
Unfortunately, my knowledge on how to set that up is literally 0 on Cent OS... updating via Auto Upgrade might always be possible in that case.