Simplepie parser errors on MAMP

I'm currently using MAMP for my local dev environment. Came across an issue when running tests, patching, etc the feeds module. My feeds keep failing when trying to use Simplepie as the parser. I would get the following error:

An AJAX HTTP error occurred. HTTP Result Code: 200 Debugging information follows. Path: /batch?id=95&op=do StatusText: OK ResponseText: Notice: Use of undefined constant DRUPAL_ROOT - assumed 'DRUPAL_ROOT' in /Users/eric/d7-feeds/sites/all/libraries/simplepie/simplepie.inc on line 738 Warning: require_once(DRUPAL_ROOT/includes/errors.inc) [function.require-once]: failed to open stream: No such file or directory in /Users/eric/d7-feeds/sites/all/libraries/simplepie/simplepie.inc on line 738 Fatal error: require_once() [function.require]: Failed opening required 'DRUPAL_ROOT/includes/errors.inc' (include_path='.:/Applications/MAMP/bin/php/php5.3.6/lib/php') in /Users/eric/d7-feeds/sites/all/libraries/simplepie/simplepie.inc on line 738

This totally threw me, after exhaustively checking everything from permissons, file paths, php settings, curl opt settings, etc, I determined that it had to be environment related. And I was right. Using 'XCache' for MAMP caching causes the errors. I'm not sure why. But setting MAMP to use APC as the cache fixed the issue.

The MAMP settings are found under the "Preferences..." button, PHP Tab, PHP Extensions box, select APC.