Symphony.

[Edit] And now it's back. Still no idea what happened.

One minute everything is working fine, the next my local copy of the site stops responding with:

Fatal error: Call to undefined method General::array_map_recursive() in /path/to/site/symphony/lib/core/class.configuration.php on line 82

I have reverted all my changes, going back to my last Git commit with no success. Even more confusing, my remote server with the same code and same database (my local copy points to it) is up and running with no issues. I'm at a loss.

That function was introduced in Symphony 2.2. Have you recently completed (or tried to complete) an upgrade? It looks like the Configuration class updated to use the function, but your General class is not the same version.

What version of Symphony are you running?

Yes, I upgraded to 2.2.5 shortly before this, though it appeared to update correctly and worked properly for an hour or two before the issue started. It hasn't been a problem since, either, so whatever was going on seems to be resolved.