I know this is an old thread, but I thought I would post this in case it helps someone else. A little while ago I started experiencing blank admin pages on a site I've had up for years. I was so puzzled because nothing has changed at all. I took a back-up of the site and did a diff to try to figure out what changed. Finally, after a bit of head scratching and trouble shooting, I discovered that my config.php file had a few extra newlines after the "?>". I took away the newlines so that there weren't any lines after ?> and voila, my admin pages were back!
I had done some changes to the config file to change the DB parameters and apparently introduced some spaces that I didn't mean to and found out that a few extra spaces in a config file can cause BIG problems. Much bigger than I ever realized.
-Kristen
Genius, I had a client site and they had recently changed their domain resulting in these errors. I was just about to spend 2 hours transferring content, users and pages to a completely fresh installation until I read this! You've saved me a lot of time, thanks.