We have a multi-site installation to manage 6 blogs. A post in one of the blogs was made 10/20/11, and a couple of posts in another blog were copied on the same date. When our blogger returned to the blogs to make posts the following week, both blogs were blank... totally blank, white page. I cannot access the dashboard, make a new post, or view the page. The other blogs are fine.
I upgraded all the blogs under the multi-site login. We do NOT access the back-end files, so there would not have been any bad code/blank code lines in the wp-config, unless somehow a blank line was inadvertently inserted into a content file when posting/copying.
I have located the backend files at the host, but I can't tell which content file is which, and quite frankly I am not confident enough in WordPress to go any further in looking at backend files.
I would be willing to contract a WordPress expert with experience in multi-site installations to help us fix this.