I updated to WordPress 3.0 this morning and had the latest version of Super Cache installed. After the update, I couldn't access the wp-admin, it was just a blank page. I removed the plug-in and all associated files and wp-admin worked fine.
I tried W3 total cache and the exact same thing happened. Once installed, no wp-admin, just a blank page. Once I removed the plug-in, the admin pages came back.
Any thoughts on what could be causing the problem with two cache plug-ins?