Down-n-dirty with Drupal Watchdog

I am dealing with some really wierd issues that need to be fixed.  The error is:

Attempt to assign property of non-object in /opt/sites/breilabs.com/dev/client/modules/node/node.module on line 1820.

In order to figure out what is going on, I am going use watchdog and start editing the core modules and basically trace my way through the problem.

First off, get a sql client and connect to your drupal db.  This will return your watchdog entries

select * from watchdog order by timestamp desc

In the various php modules that you have, you can add a call to watchdog:

   watchdog('node', 'debugging', array(), WATCHDOG_ERROR);
   watchdog('node', 'debugging 2', $node->nid, WATCHDOG_ERROR);