I just moved one of my web sites to a new server. Everything works perfectly, except for WP-Super-Cache: with it, every page request (including the back end) is coming back blank. On our old server, everything worked perfectly.
I narrowed the problem down to the "define('WP_CACHE', true);" declaration in wp-content.php. With that line there (which WP-Super-Cache inserts automatically), every single request returns a blank page, the same kind you get when there's a PHP syntax error somewhere. With the line commented out, everything returns to normal (except WP-Super-Cache doesn't work, of course).
The wp-content folder *is* writable, and I've tested that. I've also deactivated the plugin, reactivated it, cleared the cache, even have "WP Super Cache Status" status set to "Off" and the problem still persists.
The server migration was simple: copy the entire wordpress folder and database to the new server, and adjust the wp-config file.
This server is running MySQL 4.0.x and PHP 5.1.x.