What caused this blank screen across my entire installation and how do I fix it? error_log msg incl

What caused this blank screen across my entire installation and how do I fix it? error_log msg included:

[21-Jul-2012 21:14:25 UTC] PHP Fatal error: Call to a member function get() on a non-object in /home/domain/public_html/wp-includes/query.php on line 27

This is a new installation and was activating plugins network wide when this happened. I thought it was the custompress plugin that I added last, but even after deleting that folder from plugins, the problem still persists.

Ps. Once we can hopefully solve this without a fresh install, is there a list somewhere of conflicting or conflict free plugins mapped to each other?