Thanks for taking the time to report this!

http://www.mediawiki.org/wiki/Manual:How_to_debug might help to get a bit more info, and I'd also recommend to ask on https://www.mediawiki.org/wiki/Project:Support_desk

Tara: Did you ask on the support desk? Could you link to that request?

taraathan wrote:

Yes. https://www.mediawiki.org/w/index.php?title=Project:Support_desk&offset=20140914030551&limit=20#PHP_Fatal_errors_after_installing_Version_1.23.3_47970

Thanks. Fixing link: https://www.mediawiki.org/w/index.php?title=Project:Support_desk#PHP_Fatal_errors_after_installing_Version_1.23.3_47970

"The errors seem to have disappeared on their own, so this seems like a likely culprit."

taraathan wrote:

I was mistaken about the errors disappearing - I was just looking for them in the wrong place. The errors continue to appear, at a rate of between 2-8 times per day, in the error_log file in my wiki directory.

A stack trace would be useful for debugging this further.

Can you add "$wgShowExceptionDetails = true;" (without the ") to your LocalSettings.php?

(In reply to Tara Athan from comment #6)

The errors continue to appear

-> Ropen

taraathan wrote:

I have added $wgShowExceptionDetails = true; to LocalSettings.php
Where do I look for the stack trace?

taraathan wrote:

Based on my webhost's suggestion, I added

$wgCacheEpoch = '20140924154644';

to my LocalSettings.php

This has had no effect on the errors.

(In reply to taraathan@gmail.com from comment #9)

I have added $wgShowExceptionDetails = true; to LocalSettings.php
Where do I look for the stack trace?

https://www.mediawiki.org/wiki/Manual:How_to_debug states that more details (like a stack trace) should be shown on the "Fatal error" page itself.

taraathan wrote:

So far I haven't figured out what the page is that triggers this "Fatal error". The frequency pattern in the log file, and the absence of users reporting problems, suggests that it happens when some bot is crawling our site.

(In reply to taraathan@gmail.com from comment #12)

suggests that it happens when some bot is crawling our site.

You might have server logs with timestamps to compare with? :)