Debugging cron issues and errors is one of the most tricky things in Drupal. If you are dealing with a big site, with people adding nodes, inserting content which you can't allways force to be commited in the right way, and things like that, it is not unusual to find a cron broken by some "misterious" node.

Well, it is quite easy to find this "misterious" offender, just logging the cron activity. How, very easy, with my new module "cron_killing_finder".

It is published in my "Drupal SandBox": http://drupal.org/sandbox/programadoresweb/1895746

Just download it and follow the really simple instructions:

"Just activate it and go to /admin/reports/dblog. You'll find a "Node hook update_index: NID" string with the cron executions which tells you in last term which node is executed each time. If cron breaks, the last node reflected in the log will be the offender node, very simple :-)."

Hopefully it will be a new "complete" project, so you'll don't have to use git to download it.