RSS topic feeds don't appear to be working, they used to work until a day or so ago.  Everything else seems fine.

The fault thrown by "News & Announcements" RSS button is:

An error was encountered
Error: Unable to write cache file cache_feed8df782b021b768cf1a496efa6167b051f870dda0.php to cache directory. Please make sure PHP has write access to the directory '/home/flux/forum/cache/'.