Ran into some trouble and found a bunch of preg_replace with /e modifier deprecated in my error_log.

Debugging info here: http://www.pmwiki.org/wiki/PmWiki/Troubleshooting was useful.

1. Uncomment line $EnableDiag = 1; in local/config(.php)
2. Go to [wikiaddress][wikistartpage]?action=ruleset
3. Look for any lines with a file path and line number afterwards. They're easy to spot.
4. Fix, update, or remove whatever's causing the trouble. For me it was just an old skin.

• http://www.pmwiki.org/wiki/PITS/01319 - for some specific fixes.