Updated: count_cache_files() in Tiki 6.3
The error with count_cache_files() that I described below must have been caused by some problem with converting a Tiki from 5.4 to 6.3. Maybe the 5.4 version of lib/cache/cachelib.php did not actually get replaced. I have upgraded another Tiki from 6.1 to 6.3 and I did not have this problem. I had no problems at all from updating 6.1 to 6.3.
The "Tiki Cache/Sys Admin" option was getting a blank page and the error message: Call to undefined method Cachelib::count_cache_files() in .../httpdocs/tiki-admin_system.php
The change log says: cachelib: Move cache emptying logic from admin system into $cachelib->empty_cache(). Also rename the mysterious "du" function to count_cache_files as that's what it does (and improve file counting)., but I don't think that was done for 6.3.